Communication system and base station

ABSTRACT

A communication system is provided that can improve the communication capability of a communication terminal device in the case where a large number of small cells in addition to a macro cell are installed and operated. A communication terminal device (UE) is connected with a macro cell configured by a MeNB and a small cell configured by a SeNB, so that dual connectivity is performed. When receiving information for small cells, for example, emergency information from a CBC via an MME, at least one cell of the macro cell and the small cell notifies the communication terminal device connected with the at least one cell of the information for small cells.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/324,957 filed Jan. 9, 2017, which is a National Stage ofPCT/JP2015/071932 filed Aug. 3, 2015, and claims priority to JapanesePatent Application No. 2014-160482 filed Aug. 6, 2014. The entirecontents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a communication system in which radiocommunication is performed between a communication terminal device and abase station device.

BACKGROUND ART

The 3rd generation partnership project (3GPP), the standard organizationregarding the mobile communication system, is studying new communicationsystems referred to as long term evolution (LTE) regarding radiosections and system architecture evolution (SAE) regarding the overallsystem configuration including a core network and a radio accessnetwork, which will be hereinbelow collectively referred to as a networkas well (for example, see Non-Patent Documents 1 to 14). Thiscommunication system is also referred to as 3.9 generation (3.9 G)system.

As the access scheme of the LTE, orthogonal frequency divisionmultiplexing (OFDM) is used in a downlink direction and single carrierfrequency division multiple access (SC-FDMA) is used in an uplinkdirection. Differently from the wideband code division multiple access(W-CDMA), circuit switching is not provided but a packet communicationsystem alone is provided in the LTE.

The decisions by 3GPP regarding the frame configuration in the LTEsystem described in Non-Patent Document 1 (Chapter 5) will be describedwith reference to FIG. 1. FIG. 1 is a diagram illustrating aconfiguration of a radio frame used in the LTE communication system.With reference to FIG. 1, one radio frame is 10 ms. The radio frame isdivided into ten equally sized subframes. The subframe is divided intotwo equally sized slots. The first and sixth subframes contain adownlink synchronization signal (SS) per radio frame. Thesynchronization signals are classified into a primary synchronizationsignal (P-SS) and a secondary synchronization signal (S-SS).

Non-Patent Document 1 (Chapter 5) describes the decisions by 3GPPregarding the channel configuration in the LTE system. It is assumedthat the same channel configuration is used in a closed subscriber group(CSG) cell as that of a non-CSG cell.

A physical broadcast channel (PBCH) is a channel for downlinktransmission from a base station to a user equipment. A BCH transportblock is mapped to four subframes within a 40 ms interval. There is noexplicit signaling indicating 40 ms timing.

A physical control format indicator channel (PCFICH) is a channel fordownlink transmission from a base station to a user equipment. Throughthe PCFICH, the base station notifies the user equipment of the numberof orthogonal frequency division multiplexing (OFDM) symbols used forPDCCHs. The PCFICH is transmitted per subframe.

A physical downlink control channel (PDCCH) is a channel for downlinktransmission from a base station to a user equipment. The PDCCH notifiesthe resource allocation information for downlink shared channel (DL-SCH)being one of the transport channels described below, resource allocationinformation for a paging channel (PCH) being one of the transportchannels described below, and hybrid automatic repeat request (HARQ)information related to DL-SCH. The PDCCH carries an uplink schedulinggrant. The PDCCH carries acknowledgement (Ack)/negative acknowledgement(Nack) that is a response signal to uplink transmission. The PDCCH isreferred to as an L1/L2 control signal as well.

A physical downlink shared channel (PDSCH) is a channel for downlinktransmission from a base station to a user equipment. A downlink sharedchannel (DL-SCH) that is a transport channel and a PCH that is atransport channel are mapped to the PDSCH.

A physical multicast channel (PMCH) is a channel for downlinktransmission from a base station to a user equipment. A multicastchannel (MCH) that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) is a channel for uplinktransmission from a user equipment to a base station. The PUCCH carriesAck/Nack that is a response signal to downlink transmission. The PUCCHcarries a channel quality indicator (CQI) report. The CQI is qualityinformation indicating the quality of received data or channel quality.In addition, the PUCCH carries a scheduling request (SR).

A physical uplink shared channel (PUSCH) is a channel for uplinktransmission from a user equipment to a base station. An uplink sharedchannel (UL-SCH) that is one of the transport channels is mapped to thePUSCH.

A physical hybrid ARQ indicator channel (PHICH) is a channel fordownlink transmission from a base station to a user equipment. The PHICHcarries Ack/Nack that is a response signal to uplink transmission. Aphysical random access channel (PRACH) is a channel for uplinktransmission from the user equipment to the base station. The PRACHcarries a random access preamble.

A downlink reference signal (RS) is a known symbol in the LTEcommunication system. The following five types of downlink referencesignals are defined: cell-specific reference signals (CRS), MBSFNreference signals, data demodulation reference signals (DM-RS) beingUE-specific reference signals, positioning reference signals (PRS), andchannel-state information reference signals (CSI-RS). The physical layermeasurement objects of a user equipment include reference signalreceived power (RSRP).

The transport channels described in Non-Patent Document 1 (Chapter 5)will be described. A broadcast channel (BCH) among the downlinktransport channels is broadcast to the entire coverage of a base station(cell). The BCH is mapped to the physical broadcast channel (PBCH).

Retransmission control according to a hybrid ARQ (HARQ) is applied to adownlink shared channel (DL-SCH). The DL-SCH can be broadcast to theentire coverage of the base station (cell). The DL-SCH supports dynamicor semi-static resource allocation. The semi-static resource allocationis also referred to as persistent scheduling. The DL-SCH supportsdiscontinuous reception (DRX) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH).

The paging channel (PCH) supports DRX of the user equipment for enablingthe user equipment to save power. The PCH is required to be broadcast tothe entire coverage of the base station (cell). The PCH is mapped tophysical resources such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic.

The multicast channel (MCH) is used for broadcast to the entire coverageof the base station (cell). The MCH supports SFN combining of multimediabroadcast multicast service (MBMS) services (MTCH and MCCH) inmulti-cell transmission. The MCH supports semi-static resourceallocation. The MCH is mapped to the PMCH.

Retransmission control according to a hybrid ARQ (HARQ) is applied to anuplink shared channel (UL-SCH) among the uplink transport channels. TheUL-SCH supports dynamic or semi-static resource allocation. The UL-SCHis mapped to the physical uplink shared channel (PUSCH).

A random access channel (RACH) is limited to control information. TheRACH involves a collision risk. The RACH is mapped to the physicalrandom access channel (PRACH).

The HARQ will be described. The HARQ is a technique for improving thecommunication quality of a channel through combination of automaticrepeat request (ARQ) and error correction (forward error correction).The HARQ is advantageous in that error correction functions effectivelyby retransmission even for a channel whose communication qualitychanges. In particular, it is also possible to achieve further qualityimprovement in retransmission through combination of the receptionresults of the first transmission and the reception results of theretransmission.

An example of the retransmission method will be described. If thereceiver fails to successfully decode the received data, in other words,if a cyclic redundancy check (CRC) error occurs (CRC=NG), the receivertransmits “Nack” to the transmitter. The transmitter that has received“Nack” retransmits the data. If the receiver successfully decodes thereceived data, in other words, if a CRC error does not occur (CRC=OK),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data.

The logical channels described in Non-Patent Document 1 (Chapter 6) willbe described. A broadcast control channel (BCCH) is a downlink channelfor broadcast system control information. The BCCH that is a logicalchannel is mapped to the broadcast channel (BCH) or downlink sharedchannel (DL-SCH) that is a transport channel.

A paging control channel (PCCH) is a downlink channel for transmittingpaging information and system information change notifications. The PCCHis used when the network does not know the cell location of a userequipment. The PCCH that is a logical channel is mapped to the pagingchannel (PCH) that is a transport channel.

A common control channel (CCCH) is a channel for transmission controlinformation between user equipments and a base station. The CCCH is usedin the case where the user equipments have no RRC connection with thenetwork. In the downlink direction, the CCCH is mapped to the downlinkshared channel (DL-SCH) that is a transport channel. In the uplinkdirection, the CCCH is mapped to the uplink shared channel (UL-SCH) thatis a transport channel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is used for transmission ofMBMS control information for one or several MTCHs from a network to auser equipment. The MCCH is used only by a user equipment duringreception of the MBMS. The MCCH is mapped to the multicast channel (MCH)that is a transport channel.

A dedicated control channel (DCCH) is a channel that transmits dedicatedcontrol information between a user equipment and a network on apoint-to-point basis. The DCCH is used when the user equipment has anRRC connection. The DCCH is mapped to the uplink shared channel (UL-SCH)in uplink and mapped to the downlink shared channel (DL-SCH) indownlink.

A dedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink.

A multicast traffic channel (MTCH) is a downlink channel for trafficdata transmission from a network to a user equipment. The MTCH is achannel used only by a user equipment during reception of the MBMS. TheMTCH is mapped to the multicast channel (MCH).

CGI represents a cell global identifier. ECGI represents an E-UTRAN cellglobal identifier. A closed subscriber group (CSG) cell is introduced inthe LTE, and the long term evolution advanced (LTE-A) and universalmobile telecommunication system (UMTS) described below.

The closed subscriber group (CSG) cell is a cell in which subscriberswho are allowed use are specified by an operator (hereinbelow, alsoreferred to as a “cell for specific subscribers”). The specifiedsubscribers are allowed to access one or more cells of a public landmobile network (PLMN). One or more cells to which the specifiedsubscribers are allowed access are referred to as “CSG cell(s)”. Notethat access is restricted in the PLMN.

The CSG cell is part of the PLMN that broadcasts a specific CSG identity(CSG ID; CSG-ID) and broadcasts “TRUE” in a CSG indication. Theauthorized members of the subscriber group who have registered inadvance access the CSG cells using the CSG-ID that is the accesspermission information.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in the LTE communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier.

The locations of user equipments are tracked based on an area composedof one or more cells. The locations are tracked for enabling trackingthe locations of user equipments and calling user equipments, in otherwords, incoming calling to user equipments even in an idle state. Anarea for tracking locations of user equipments is referred to as atracking area.

3GPP is studying base stations referred to as Home-NodeB (Home-NB; HNB)and Home-eNodeB (Home-eNB; HeNB). HNB/HeNB is a base station for, forexample, household, corporation, or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 3 discloses three different modes ofthe access to the HeNB and HNB. Specifically, an open access mode, aclosed access mode, and a hybrid access mode are disclosed.

The individual modes have the following characteristics. In the openaccess mode, the HeNB and HNB are operated as a normal cell of a normaloperator. In the closed access mode, the HeNB and HNB are operated as aCSG cell. The CSG cell is a CSG cell where only CSG members are allowedaccess. In the hybrid access mode, the HeNB and HNB are operated as CSGcells where non-CSG members are allowed access at the same time. Inother words, a cell in the hybrid access mode (also referred to as ahybrid cell) is a cell that supports both the open access mode and theclosed access mode.

In 3GPP, among all physical cell identities (PCIs) is a range of PCIsreserved by the network for use by CSG cells (see Chapter 10.5.1.1 ofNon-Patent Document 1). Division of the PCI range is also referred to asPCI split. The information about PCI split (also referred to as PCIsplit information) is broadcast in the system information from a basestation to user equipments being served thereby. Being served by a basestation means taking the base station as a serving cell.

Non-Patent Document 4 discloses the basic operation of a user equipmentusing PCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs, for example,using all 504 codes. In contrast, the user equipment that has the PCIsplit information is capable of performing cell search using the PCIsplit information.

Further, 3GPP is pursuing specifications standard of long term evolutionadvanced (LTE-A) as Release 10 (see Non-Patent Documents 5 and 6). TheLTE-A is based on the LTE radio communication system and is configuredby adding several new techniques to the system.

Carrier aggregation (CA), which is also referred to as “aggregation”, isstudied for the LTE-A system, in which two or more component carriers(CCs) are aggregated to support wider transmission bandwidths up to 100MHz.

In the case where CA is configured, a UE has a single RRC connectionwith a network (NW). In RRC connection, one serving cell provides NASmobility information and security input. This cell is referred to as aprimary cell (PCell). In downlink, a carrier corresponding to PCell is adownlink primary component carrier (DL PCC). In uplink, a carriercorresponding to PCell is an uplink primary component carrier (UL PCC).

A secondary cell (SCell) is configured to form a serving cell group witha PCell, in accordance with the UE capability. In downlink, a carriercorresponding to SCell is a downlink secondary component carrier (DLSCC). In uplink, a carrier corresponding to SCell is an uplink secondarycomponent carrier (UL SCC).

A serving cell group of one PCell and one or more SCells is configuredfor one UE.

The new techniques in the LTE-A include the technique of supportingwider bands (wider bandwidth extension) and the coordinated multiplepoint transmission and reception (CoMP) technique. The CoMP studied forLTE-A in 3GPP is described in Non-Patent Document 7.

3GPP is developing specifications of Release 12. In the specificationsof Release 12, the use of small eNBs configuring small cells is studiedto satisfy a tremendous volume of traffic in the future. In an exampletechnique under study, a large number of small eNBs are installed toconfigure a large number of small cells, thus increasing spectralefficiency for increased communication capacity.

The traffic flow of a mobile network is on the rise, and thecommunication rate is also increasing. It is expected that thecommunication rate will be further increased when the operations of theLTE and the LTE-A are fully initiated, leading to an increase in trafficflow.

PRIOR ART DOCUMENTS Non-Patent Documents

Non-Patent Document 1: 3GPP TS 36.300 V12.1.0

Non-Patent Document 2: 3GPP TS 36.304 V12.0.0

Non-Patent Document 3: 3GPP S1-083461

Non-Patent Document 4: 3GPP R2-082899

Non-Patent Document 5: 3GPP TR 36.814 V9.0.0

Non-Patent Document 6: 3GPP TR 36.912 V10.0.0

Non-Patent Document 7: 3GPP TR 36.819 V11.2.0

Non-Patent Document 8: 3GPP TS 36.141 V12.4.0

Non-Patent Document 9: 3GPP TR 36.842 V12.0.0

Non-Patent Document 10: 3GPP TS 23.041 V12.5.0

Non-Patent Document 11: 3GPP R2-142471

Non-Patent Document 12: 3GPP R2-142027

Non-Patent Document 13: 3GPP TS 23.401 V12.4.0

Non-Patent Document 14: 3GPP TS 36.211 V12.1.0

SUMMARY OF INVENTION Problems to be Solved by the Invention

Installing and operating a large number of small cells in addition to amacro cell causes a reduction in mobility capability and an increase ininterference. To solve these problems, 3GPP is studying a dualconnectivity (abbreviated as DC) technique. It is studied for DC that aUE uses a macro cell and a small cell for communication. Specifically,3GPP is studying that the mobility capability of a UE is secured by themacro cell and that a resource of the macro cell and a resource of thesmall cell are used together to increase a throughput in datacommunication.

Unfortunately, the application of DC to a conventional technique withoutany contrivance may prevent the technique from being achieved. Examplesof such a technique include a public warning system (PWS) that is awarning information notification service, an emergency service, and a UErequested bearer modification. In the PWS, the UE during DC cannot benotified of warning information for small cells. In the emergencyservice, in execution of DC, a secondary eNB may reject the execution ofDC considering the status of the eNB. In the UE requested bearermodification, the bearer subjected to DC cannot be modified. A method ofsolving such a problem is thus required.

Considering that a large number of small cells in addition to a macrocell are installed and operated in DC, a further improvement in mobilitycapability is desired. For example, when the UE moves within a macrocell and changes a small cell, the method of deriving the location andmoving status of the UE in a conventional technique cannot change asmall cell optimally, thus reducing the mobility capability.

3GPP is also studying a technique for communication using a plurality ofcells (points) or a plurality of antennas for a UE, such as CoMP ormultiple input and multiple output (MIMO). This technique uses cells orantennas in a coordinated manner to reduce an influence of interference,thus increasing a throughput.

Considering that a large number of small cells in addition to a macrocell are installed and operated in the techniques such as CoMP and MIMO,however, a technique for further improving mobility capability andreducing interference or a technique of enabling optimum scheduling by acell that is a UE's moving destination to increase a throughput isrequired.

The present invention has an object to provide a communication systemcapable of improving the communication capability of a communicationterminal device in the installation and operation of a large number ofsmall cells in addition to a macro cell.

Means to Solve the Problems

A communication system according to the present invention includes acommunication terminal device and base station devices configuring cellscapable of radio communication with the communication terminal device.The cells include a macro cell and a small cell. The macro cell has acoverage in which communication with the communication terminal deviceis enabled and which is relatively large. The small cell is providedsuch that at least a part of the coverage of the small cell overlaps thecoverage of the macro cell. The coverage of the small cell is relativelysmall. When the communication terminal device is connected to the macrocell and the small cell, upon receipt of information for small cellsdirected to the small cell from a higher-layer device, at least one cellof the macro cell and the small cell notifies the communication terminaldevice connected with the at least one cell of the information for smallcells.

EFFECTS OF THE INVENTION

In the communication system according to the present invention, thecommunication terminal device is connected to the macro cell and thesmall cell for dual connectivity. At least one cell of the macro celland the small cell notifies the communication terminal device connectedwith the at least one cell of the information for small cells from thehigher-layer device. This enables the communication terminal device toreceive the information for small cells. The communication capability ofthe communication terminal device can thus be improved in the operationof a large number of small cells in addition to a macro cell.

These and other objects, features, aspects and advantages of the presentinvention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a radio frame foruse in an LTE communication system.

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 700 under discussion of 3GPP.

FIG. 3 is a block diagram showing a configuration of a user equipment 71shown in FIG. 2, which is a user equipment according to the presentinvention.

FIG. 4 is a block diagram showing a configuration of a base station 72shown in

FIG. 2, which is a base station according to the present invention.

FIG. 5 is a block diagram showing a configuration of an MME according tothe present invention.

FIG. 6 is a flowchart showing an outline from a cell search to an idlestate operation performed by a user equipment (UE) in the LTEcommunication system.

FIG. 7 shows the concept of a cell configuration in which macro eNBs andsmall eNBs coexist.

FIG. 8 shows an example of a cell configuration when a macro cell andsmall cells are overlaid on one another.

FIG. 9 shows an example flow of a PWS message in a communication systemof a first embodiment.

FIG. 10 shows an example of a sequence of a PWS message notificationprocess in the communication system of the first embodiment.

FIG. 11 shows another example of the sequence of the PWS messagenotification process in the communication system of the firstembodiment.

FIG. 12 shows an example flow of a PWS message in a communication systemof a first modification of the first embodiment.

FIG. 13 shows an example of a sequence of a PWS message notificationprocess in the communication system of the first modification of thefirst embodiment.

FIG. 14 shows another example of the sequence of the PWS messagenotification process in the communication system of the firstmodification of the first embodiment.

FIG. 15 shows an example flow of a PWS message in a communication systemof a second modification of the first embodiment.

FIG. 16 shows an example of a sequence of a PWS message notificationprocess in the communication system of the second modification of thefirst embodiment.

FIG. 17 shows another example of the sequence of the PWS messagenotification process in the communication system of the secondmodification of the first embodiment.

FIG. 18 shows an example of a sequence of a PWS message notificationprocess in a communication system of a third modification of the firstembodiment.

FIG. 19 shows another example of the sequence of the PWS messagenotification process in the communication system of the thirdmodification of the first embodiment.

FIG. 20 shows an example flow of a PWS message in a communication systemof a fourth modification of the first embodiment.

FIG. 21 shows an example of a sequence of a DC execution process to anemergency bearer in a communication system of a second embodiment.

FIG. 22 shows an example of a sequence of a UE-activated DC bearermodification process in a communication system of a third embodiment.

FIG. 23 shows another example of the sequence of the UE-activated DCbearer modification process in the communication system of the thirdembodiment.

FIG. 24 shows an example of a sequence of a SCG cell measurement processin a communication system of a first modification of a fourthembodiment.

FIG. 25 shows the concept of UL CoMP under discussion of 3GPP.

FIG. 26 shows an example of an operation of DC in a communication systemof a first modification of a fifth embodiment.

FIG. 27 shows another example of the operation of DC in thecommunication system of the first modification of the fifth embodiment.

FIG. 28 shows the concept of a problem to be solved in a sixthembodiment.

FIG. 29 shows an example of a sequence of an SRS reception process in acommunication system of the sixth embodiment.

FIG. 30 shows another example of the sequence of the SRS receptionprocess in the communication system of the sixth embodiment.

FIG. 31 is a diagram for showing a difference between an SRS receptionstart threshold and a HO start threshold with respect to a measurementreport value.

FIG. 32 shows an example of antenna control in a communication system ofa seventh embodiment.

DESCRIPTION OF EMBODIMENTS

First Embodiment

FIG. 2 is a block diagram showing an overall configuration of an LTEcommunication system 700, which is under discussion of 3GPP. FIG. 2 willbe described. A radio access network is referred to as an evolveduniversal terrestrial radio access network (E-UTRAN) 70. A userequipment device (hereinbelow, referred to as a “user equipment (UE)”)71, which is a communication terminal device, is capable of radiocommunication with a base station device (hereinbelow, referred to as a“base station (E-UTRAN NodeB: eNB)”) 72 and transmits and receivessignals through radio communication.

The E-UTRAN is composed of one or more base stations 72, provided that acontrol protocol for a user equipment 71 such as a radio resourcecontrol (RRC), and user planes such as a packet data convergenceprotocol (PDCP), radio link control (RLC), medium access control (MAC),and physical layer (PHY) are terminated in the base station 72.

The control protocol radio resource control (RRC) between the userequipment 71 and the base station 72 performs broadcast, paging, RRCconnection management, and the like. The states of the base station 72and the user equipment 71 in RRC are classified into RRC_IDLE andRRC_CONNECTED.

In RRC_IDLE, public land mobile network (PLMN) selection, systeminformation (SI) broadcast, paging, cell re-selection, mobility, and thelike are performed. In RRC_CONNECTED, the user equipment has RRCconnection and is capable of transmitting and receiving data to and froma network. In RRC_CONNECTED, the user equipment performs, for example,handover (HO) and measurement of a neighbor cell.

The base stations 72 are classified into eNBs 76 and Home-eNBs 75. Thecommunication system 700 includes an eNB group 72-1 including aplurality of eNBs 76 and a Home-eNB group 72-2 including a plurality ofHome-eNBs 75. A system composed of an evolved packet core (EPC) being acore network and an E-UTRAN 70 being a radio access network is referredto as an evolved packet system (EPS). The EPC being a core network andthe E-UTRAN 70 being a radio access network may be collectively referredto as a “network”.

The eNB 76 is connected to an MME/S-GW unit (hereinbelow, also referredto as an “MME unit”) 73 including a mobility management entity (MME), aserving gateway (S-GW), or an MME and an S-GW by means of an S1interface, and control information is communicated between the eNB 76and the MME unit 73. A plurality of MME units 73 may be connected to oneeNB 76. The eNBs 76 are connected to each other by means of an X2interface, and control information is communicated between the eNBs 76.

The Home-eNB 75 is connected to the MME unit 73 by means of an S1interface, and control information is communicated between the Home-eNB75 and the MME unit 73. A plurality of Home-eNBs 75 are connected to oneMME unit 73. Or, the Home-eNBs 75 are connected to the MME units 73through a Home-eNB gateway (HeNBGW) 74. The Home-eNB 75 is connected tothe HeNBGW 74 by means of an S1 interface, and the HeNBGW 74 isconnected to the MME unit 73 by means of an S1 interface.

One or more Home-eNBs 75 are connected to one HeNBGW 74, and informationis communicated therebetween through an S1 interface. The HeNBGW 74 isconnected to one or more MME units 73, and information is communicatedtherebetween through an S1 interface.

The MME units 73 and HeNBGW 74 are higher-layer entities, specifically,higher nodes, and control the connections between the user equipment(UE) 71 and the eNB 76 and the Home-eNB 75 that are base stations. TheMME units 73 configure an EPC being a core network. The base station 72and the HeNBGW 74 configure an E-UTRAN 70.

Further, 3GPP is studying the configuration below. The X2 interfacebetween the Home-eNBs 75 is supported. In other words, the Home-eNBs 75are connected to each other by means of an X2 interface, and controlinformation is communicated between the Home-eNBs 75. The HeNBGW 74appears to the MME unit 73 as the Home-eNB 75. The HeNBGW 74 appears tothe Home-eNB 75 as the MME unit 73.

The interfaces between the Home-eNBs 75 and the MME units 73 are thesame, which are the S1 interfaces, in both cases where the Home-eNB 75is connected to the MME unit 73 through the HeNBGW 74 and the Home-eNB75 is directly connected to the MME unit 73.

The base station device 72 may configure a single cell or a plurality ofcells. Each cell has a range predetermined as a coverage in which thecell can communicate with a communication terminal device and performsradio communication with the communication terminal device within thecoverage. In the case where one base station device configures aplurality of cells, every cell is configured to communicate with theuser equipment 71.

FIG. 3 is a block diagram showing a configuration of the user equipment71 of FIG. 2, which is a user equipment according to the presentinvention. The transmission process of the user equipment 71 shown inFIG. 3 will be described. First, a transmission data buffer unit 803stores the control data from a protocol processing unit 801 and the userdata from an application unit 802. The data stored in the transmissiondata buffer unit 803 is passed to an encoding unit 804 and is subjectedto an encoding process such as error correction. There may exist thedata output from the transmission data buffer unit 803 directly to amodulating unit 805 without the encoding process. The data encoded bythe encoding unit 804 is modulated by the modulating unit 805. Themodulated data is converted into a baseband signal, and the basebandsignal is output to a frequency converting unit 806 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 807 to the basestation 72.

The user equipment 71 executes the reception procedure as follows. Theradio signal from the base station 72 is received by the antenna 807.The received signal is converted from a radio reception frequency into abaseband signal by the frequency converting unit 806 and is thendemodulated by a demodulating unit 808. The demodulated data is passedto a decoding unit 809 and is subjected to a decoding process such aserror correction. Among the pieces of decoded data, the control data ispassed to the protocol processing unit 801, and the user data is passedto the application unit 802. A series of processes by the user equipment71 is controlled by a control unit 810. This means that, though notshown in FIG. 3, the control unit 810 is connected to the individualunits 801 to 809.

FIG. 4 is a block diagram showing a configuration of the base station 72of FIG. 2, which is a base station according to the present invention.The transmission process of the base station 72 shown in FIG. 4 will bedescribed. An EPC communication unit 901 performs data transmission andreception between the base station 72 and the EPC (such as the MME unit73), HeNBGW 74, and the like. A communication with another base stationunit 902 performs data transmission and reception to and from anotherbase station. The EPC communication unit 901 and the communication withanother base station unit 902 each transmit and receive information toand from a protocol processing unit 903. The control data from theprotocol processing unit 903, and the user data and the control datafrom the EPC communication unit 901 and the communication with anotherbase station unit 902 are stored in a transmission data buffer unit 904.

The data stored in the transmission data buffer unit 904 is passed to anencoding unit 905 and is then subjected to an encoding process such aserror correction. There may exist the data output from the transmissiondata buffer unit 904 directly to a modulating unit 906 without theencoding process. The encoded data is modulated by the modulating unit906. The modulated data is converted into a baseband signal, and thebaseband signal is output to a frequency converting unit 907 and is thenconverted into a radio transmission frequency. After that, atransmission signal is transmitted from an antenna 908 to one or moreuser equipments 71.

The reception procedure of the base station 72 is executed as follows. Aradio signal from one or more user equipments 71 is received through theantenna 908. The received signal is converted from a radio receptionfrequency into a baseband signal by the frequency converting unit 907,and is then demodulated by a demodulating unit 909. The demodulated datais passed to a decoding unit 910 and is then subjected to a decodingprocess such as error correction. Among the pieces of decoded data, thecontrol data is passed to the protocol processing unit 903, the EPCcommunication unit 901, or the communication with another base stationunit 902, and the user data is passed to the EPC communication unit 901and the communication with another base station unit 902. A series ofprocesses by the base station 72 is controlled by a control unit 911.This means that, though not shown in FIG. 4, the control unit 911 isconnected to the individual units 901 to 910.

FIG. 5 is a block diagram showing a configuration of the MME accordingto the present invention. FIG. 5 shows the configuration of an MME 73 aincluded in the MME unit 73 shown in FIG. 2 described above. A PDN GWcommunication unit 1001 performs data transmission and reception betweenthe MME 73 a and the PDN GW. A base station communication unit 1002performs data transmission and reception between the MME 73 a and thebase station 72 by means of the S1 interface. In the case where the datareceived from the PDN GW is user data, the user data is passed from thePDN GW communication unit 1001 to the base station communication unit1002 via a user plane communication unit 1003 and is then transmitted toone or more base stations 72. In the case where the data received fromthe base station 72 is user data, the user data is passed from the basestation communication unit 1002 to the PDN GW communication unit 1001via the user plane communication unit 1003 and is then transmitted tothe PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is passed from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data is passedfrom the base station communication unit 1002 to the control planecontrol unit 1005.

A HeNBGW communication unit 1004 is provided in the case where theHeNBGW 74 is provided, which performs data transmission and receptionbetween the MME 73 a and the HeNBGW 74 by means of the interface (IF)according to an information type. The control data received from theHeNBGW communication unit 1004 is passed from the HeNBGW communicationunit 1004 to the control plane control unit 1005. The processing resultof the control plane control unit 1005 is transmitted to the PDN GW viathe PDN GW communication unit 1001. The processing results of thecontrol plane control unit 1005 are transmitted to one or more basestations 72 by means of the S1 interface via the base stationcommunication unit 1002, and is transmitted to one or more HeNBGWs 74via the HeNBGW communication unit 1004.

The control plane control unit 1005 includes a NAS security unit 1005-1,an SAE bearer control unit 1005-2, and an idle state mobility managingunit 1005-3, and performs an overall process for the control plane. TheNAS security unit 1005-1 provides, for example, security of a non-accessstratum (NAS) message. The SAE bearer control unit 1005-2 manages, forexample, a system architecture evolution (SAE) bearer. The idle statemobility managing unit 1005-3 performs, for example, mobility managementof an idle state (LTE-IDLE state, which is merely referred to as idle aswell), generation and control of a paging signal in the idle state,addition, deletion, and update of and search for a tracking area of oneor more user equipments 71 being served thereby, and tracking area listmanagement.

The MME 73 a distributes a paging signal to one or more base stations72. In addition, the MME 73 a performs mobility control of an idlestate. When the user equipment is in the idle state and active state,the MME 73 a manages a list of tracking areas. The MME 73 a begins apaging protocol by transmitting a paging message to the cell belongingto a tracking area in which the UE is registered. The idle statemobility managing unit 1005-3 may manage the CSG of the Home-eNBs 75 tobe connected to the MME 73 a, CSG-IDs, and a whitelist.

An example of a cell search method in a mobile communication system willbe described next. FIG. 6 is a flowchart showing an outline from a cellsearch to an idle state operation performed by a user equipment (UE) inthe LTE communication system. When starting a cell search, in step ST1,the user equipment synchronizes slot timing and frame timing by aprimary synchronization signal (P-SS) and a secondary synchronizationsignal (S-SS) transmitted from a neighbor base station.

The P-SS and S-SS are collectively referred to as synchronizationsignals (SSs). Synchronization codes, which correspond one-to-one toPCIs assigned per cell, are assigned to the synchronization signals(SSs). The number of PCIs is currently studied in 504 ways. The 504 waysof PCIs are used for synchronization, and the PCIs of the synchronizedcells are detected (specified).

In step ST2, for the synchronized cells, the user equipment next detectsa cell-specific reference signal (CRS) being a reference signal (RS)transmitted from the base station per cell and measures the referencesignal received power (RSRP). The codes corresponding one-to-one to thePCIs are used for the reference signal (RS). Separation from anothercell is enabled by correlation using the code. The code for RS of thecell is derived from the PCI specified in step ST1, so that the RS canbe detected and the RS received power can be measured.

In step ST3, the user equipment then selects the cell having the best RSreceived quality, for example, the cell having the highest RS receivedpower, that is, the best cell, from one or more cells that have beendetected up to step ST2.

In step ST4, the user equipment then receives the PBCH of the best celland obtains the BCCH that is the broadcast information. A masterinformation block (MIB) containing the cell configuration information ismapped to the BCCH over the PBCH. The MIB is accordingly obtained byobtaining the BCCH through reception of the PBCH. Examples of the MIBinformation include the downlink (DL) system bandwidth, which is alsoreferred to as a transmission bandwidth configuration (dl-bandwidth),the number of transmission antennas, and a system frame number (SFN).

In step ST5, the user equipment then receives the DL-SCH of the cellbased on the cell configuration information of the MIB, to therebyobtain a system information block (SIB) 1 of the broadcast informationBCCH. The SIB1 contains the information about the access to the cell,information about cell selection, and scheduling information on anotherSIB (SIBk; k is an integer equal to or greater than two). In addition,the SIB1 contains a tracking area code (TAC).

In step ST6, the user equipment then compares the TAC of the SIB1received in step ST5 with the TAC portion of a tracking area identity(TAI) in the tracking area list that has already been possessed by theuser equipment. The tracking area list is also referred to as a TAIlist. TAI is the identification information for identifying trackingareas and is composed of a mobile country code (MCC), a mobile networkcode (MNC), and a tracking area code (TAC). MCC is a country code. MNCis a network code. TAC is the code number of a tracking area.

If the result of the comparison of step ST6 shows that the TAC receivedin step ST5 is identical to the TAC included in the tracking area list,the user equipment enters an idle state operation in the cell. If theresult of the comparison shows that the TAC received in step ST5 is notincluded in the tracking area list, the user equipment requests a corenetwork (EPC) including MME and the like to change a tracking areathrough the cell for performing tracking area update (TAU).

The device configuring a core network (hereinbelow, also referred to asa “core-network-side device”) updates the tracking area list based on anidentification number (such as UE-ID) of a user equipment transmittedfrom the user equipment together with a TAU request signal. Thecore-network-side device transmits the updated tracking area list to theuser equipment. The user equipment rewrites (updates) the TAC list ofthe user equipment based on the received tracking area list. After that,the user equipment enters the idle state operation in the cell.

Widespread use of smartphones and tablet terminals explosively increasestraffic in cellular radio communications, causing a fear of insufficientradio resources all over the world. To increase spectral efficiency,thus, it is studied to downsize cells for spatial separation.

In the conventional configuration of cells, the cell configured by aneNB has a relatively-large-range coverage. Conventionally, cells areconfigured such that relatively-large-range coverages of a plurality ofcells configured by a plurality of eNBs cover a certain area.

When cells are downsized, the cell configured by an eNB has anarrow-range coverage compared with the coverage of a cell configured bya conventional eNB. Thus, in order to cover a certain area as in theconventional case, a larger number of downsized eNBs than theconventional eNBs are required.

In the description below, a “macro cell” refers to a cell whose coverageis relatively large, that is, whose coverage area is relatively large,such as a cell configured by a conventional eNB, and a “macro eNB”refers to an eNB configuring a macro cell. A “small cell” refers to acell whose coverage is relatively small, that is, whose coverage area isrelatively small, such as a downsized cell, and a “small eNB” refers toan eNB configuring a small cell.

The macro eNB may be, for example, a “wide area base station” describedin Non-Patent Document 8.

The small eNB may be, for example, a low power node, local area node, orhotspot. Alternatively, the small eNB may be a pico eNB configuring apico cell, a femto eNB configuring a femto cell, HeNB, remote radio head(RRH), remote radio unit (RRU), remote radio equipment (RRE), or relaynode (RN). Still alternatively, the small eNB may be a “local area basestation” or “home base station” described in Non-Patent Document 8.

FIG. 7 shows the concept of a cell configuration in which macro eNBs andsmall eNBs coexist. The macro cell configured by a macro eNB has arelatively-large-range coverage 1301. The small cell configured by asmall eNB has a coverage 1302 whose range is smaller than the coverageof the coverage 1301 of the macro eNB (macro cell).

When a plurality of eNBs coexist, the coverage of the cell configured byan eNB may be included in the coverage of the cell configured by anothereNB. In the cell configuration shown in FIG. 7, as indicated byreference “1304” or “1305”, the coverage 1302 of the small cellconfigured by a small eNB may be included in the coverage 1301 of themacro cell configured by a macro eNB.

As indicated by reference “1305”, the coverages 1302 of a plurality of,for example, two small cells may be included in the coverage 1301 of onemacro cell. A user equipment (UE) 1303 is included in, for example, thecoverage 1302 of the small cell and performs communication via the smallcell.

In the cell configuration shown in FIG. 7, as indicated by reference“1306”, the coverage 1301 of the macro cell configured by a macro eNBmay complicatedly overlap the coverages 1302 of the small cellsconfigured by small eNBs.

As indicated by reference “1307”, the coverage 1301 of the macro cellconfigured by a macro eNB may not overlap the coverages 1302 of thesmall cells configured by small eNBs.

Further, as indicated by reference “1308”, the coverages 1302 of a largenumber of small cells configured by a large number of small eNBs may beconfigured in the coverage 1301 of one macro cell configured by onemacro eNB.

It is studied in the operation of a small cell to improve a throughputby configuring a small cell in an area of heavy traffic within thecoverage of a macro cell, that is, by placing (overlaying) a small cellon a macro cell.

FIG. 8 shows an example of a cell configuration in which a macro celland small cells are overlaid on one another. With reference to FIG. 8,the coverage of a macro cell is indicated by reference “1301” and thecoverage of a small cell is indicated by reference “1302” as in FIG. 7.

3GPP is studying dual connectivity (abbreviated as DC) in which a UE isconnected to both a macro cell and a small cell in the cellconfiguration as shown in FIG. 8 (see Non-Patent Document 9). In thecontrol plane (C-plane) for a UE performing DC, a secondary eNB (SeNB)is connected via a master eNB (MeNB) to an MME.

Two architectures are mainly studied in the user plane (U-plane) for theUE performing DC: one of them is an architecture in which a SeNB isdirectly connected to a S-GW (hereinbelow also referred to as“architecture 1A”), and the other is an architecture in which a SeNB isconnected via a MeNB to a S-GW (hereinbelow also referred to as“architecture 3C”).

Herein, the MeNB is an eNB configuring a macro cell in DC. The SeNB isan eNB configuring a small cell in DC. A cell group configured by theMeNB is referred to as “MCG”, and a cell group configured by the SeNB isreferred to as “SCG”. A cell in the MCG is referred to as an “MCG cell”,and a cell in the SCG is referred to as an “SCG cell”. A cell thattransmits the PUCCH in the MCG is referred to as “PCell”. A special cellthat transmits the PUCCH in the SCG is referred to as “SPCell”. TheSPCell has some of the functions of the PCell.

A problem to be solved in the first embodiment and a solution to theproblem will be described below. The public warning system (PWS) is asystem that notifies a UE located in a specific area of a warningmessage (see Non-Patent Document 10). Examples of the PWS include anEarthquake and Tsunami Warning System (ETWS), Commercial Mobile AlertSystem (CMAS), European Public Warning System (EU-ALERT), and KoreanPublic Alert System (KPAS).

The PWS supports not only a UE in RRC_IDLE but also a UE inRRC_CONNECTED because of the importance of a message to be notified. Themessage in the PWS (hereinbelow also referred to as a “PWS message”) isnotified to the eNB by the MME via an S1-MME that is an interface of thecontrol plane (C-Plane). The PWS message corresponds to the informationfor small cells that is directed from a higher-layer entity to a smallcell. Examples of the higher-layer entity include a cell broadcastentity (CBE), a cell broadcast centre (CBC), and an MME.

In DC under discussion of 3GPP, the SeNB is not directly connected withthe MME in the control plane (C-Plane) of the UE during DC. Inapplication of the PWS described above to DC, the UE performing DC usingthe SeNB is not accordingly to be notified of the PWS message for theSeNB, and the UE cannot receive a PWS message for the SeNB.

As to how to handle the PWS in DC, 3GPP has discussed only that the UEduring DC receives a PWS message for the MeNB and has not discussed howthe UE during DC receives a PWS message for the SeNB (see Non-PatentDocuments 11 and 12).

The PWS is targeted for a specific area, and accordingly, even when theSeNB and the MeNB are overlaid on each other, the PWS message for theSeNB may differ from the PWS message for the MeNB. Enabling the UElocated within the coverage of the SeNB to receive the PWS message forthe SeNB is thus effective for the UE.

The first embodiment will disclose the method of enabling a UEperforming DC using a SeNB to receive a PWS message for the SeNB.

The solution in the first embodiment will be described below. The SeNBtransmits a PWS message for the SeNB to the UE during DC. The UEperforming DC using the SeNB receives the PWS message for the SeNB.

When the PWS message is notified to a specific SCG cell or specific SCGcells, the SeNB used in DC transmits a PWS message for its own SCG cellto the UE performing DC using its own SCG cell. The UE performing DCusing the SCG cell receives the PWS message for the SCG cell.

The PWS message notification method will be described. FIG. 9 shows anexample flow of a PWS message in a communication system of the firstembodiment. With reference to FIG. 9, the flow of the PWS message isindicated by bold arrows 106, 107, and 108.

The PWS message is notified to a cell broadcast centre (CBC) 101 by acell broadcast entity (CBE, not shown). The CBC 101 notifies an MME 102of the PWS message notified by the CBE as indicated by the arrow 106.

The MME 102 notifies an eNB of the PWS message notified by the CBC 101.Specifically, the MME 102 notifies a SeNB 104 of the PWS message asindicated by the arrow 107. The MME 102 also notifies a MeNB 103 of thePWS message. When its own cell is being used in DC, that is, when theeNB is the SeNB 104, the eNB notifies a UE 105 performing DC using itsown cell of the PWS message notified by the MME 102 as indicated by thearrow 108.

The MME 102 and the MeNB 103 are connected by an interface 111. An S1interface is used as the interface 111 between the MME 102 and the MeNB103. Indicated herein is an interface to the UE 105 during DC.

The MeNB 103 and the SeNB 104 are connected by an interface 112. An X2or Xn interface is used as the interface 112 between the MeNB 103 andthe SeNB 104. Indicated herein is an interface to the UE 105 during DC.

For the SeNB 104 to notify the UE 105 performing DC using the cell ofthe SeNB 104 of a PWS message, the SCG cell may include a PWS message inan SIB and broadcast the SIB.

The SIB including the PWS message (hereinbelow also referred to as “SIBfor PWS message”) may be a newly provided SIB or an existing SIB.Examples of the existing SIB including a PWS message include SIB10 andSIB11 for ETWS and SIB12 for CMAS.

The method in which a SCG cell broadcasts a PWS message to a UE beingserved thereby is applicable as the method in which a SCG cell notifiesa UE during DC of a PWS message. The SCG cell has to notify a UE beingserved thereby of a PWS message. This notification is made throughbroadcasting.

The SCG cell also notifies a UE performing DC using the SCG cell of aPWS message by the method in which the SCG cell broadcasts a PWS messageto a UE being served thereby, thus eliminating the need for additionalnew process. This prevents the function of the SeNB from becomingcomplicated, reducing malfunctions.

The UE performing DC using the SCG cell receives the SIB for PWS messagethat is broadcast from the SCG cell. The PWS message is included in theSIB for PWS message to be broadcast, and accordingly, the UE receivesthe SIB for PWS message to receive the PWS message contained in the SIBfor PWS message.

A PWS indication may be provided to show the UE during DC that the PWSmessage has been broadcast. The PWS indication corresponds to broadcastindication information indicating that the information for small cellshas been broadcast. The PWS indication is notified to the UE during DCbefore the PWS message. Upon receipt of the PWS indication, the UEduring DC receives the SIB including the PWS message of the SCG cell.With reference to FIG. 9, the flow of the PWS indication is indicated byarrows 109 and 110.

When receiving the PWS message for the SeNB 104 from the MME 102, theSeNB 104 notifies the UE 105 of the PWS indication. The following two,(1) and (2), will be disclosed as specific examples of the PWSindication notification method.

(1) The SeNB 104 directly notifies the UE 105 during DC as indicated bythe arrow 110.

(2) The SeNB 104 notifies the UE 105 during DC via the MeNB 103 asindicated by the arrow 109.

The case where the notification method (1) is applied as the PWSindication notification method will be described. The SeNB 104 that hasreceived the PWS message from the MME 102 specifies a SCG cell to whichthe SeNB 104 transmits the PWS message. The SCG cell includes the PWSindication in a paging message and notifies a UE being served thereby ofthe message. The SCG cell also notifies the UE during DC of the pagingmessage including the PWS indication. The SCG cell broadcasts a PWSmessage.

The UE performing DC using the SCG cell receives the paging message fromthe SCG cell to receive the PWS indication contained in the pagingmessage.

The PWS indication may be a newly provided indication or an existingindication. Examples of the existing indication include an ETWSindication for ETWS and a CMAS indication for CMAS.

Upon receipt of the PWS indication contained in the paging message, theUE performing DC using the SCG cell receives the SIB including the PWSmessage of the SCG cell.

The SIB including a PWS message may be determined statically in advance.The SIB including a PWS message may be determined in specifications.

The UE performing DC using the SCG cell receives SIB (SIB1) includingscheduling information for the reception of the SIB including the PWSmessage. The UE during DC that has received the SIB1 of the SCG celluses the scheduling information to receive the SIB including the PWSmessage.

FIG. 10 shows an example of a sequence of a PWS message notificationprocess in the communication system of the first embodiment. FIG. 10shows an example of the case where the notification method (1) describedabove is applied as the PWS indication notification method.

In step ST1001, the UE, the MeNB, and the MME perform a registrationprocedure. In the registration procedure, specifically, the UE performsregistration with the MME via the MeNB. After the completion of theregistration procedure, the UE enters the RRC_CONNECTED state with theMeNB.

In step ST1002, the MeNB activates a procedure for adding a SeNB(hereinbelow also referred to as a “SeNB addition procedure”) to performDC to the UE. As a result, the SeNB addition procedure is performedamong the MeNB, the UE, and the SeNB. Details of the SeNB additionprocedure are disclosed in, for example, Non-Patent Document 9. In theSeNB addition procedure, the UE is synchronized with a SCG cell to beadded.

In step ST1003, the UE that has performed the SeNB addition procedureand has been synchronized with the SCG cell to be added receives a PCHto which the paging message of the SCG cell is mapped. In thisembodiment, the UE intermittently receives a PCH to which the pagingmessage of the SCG cell is mapped.

The UE may receive the information about the PCH transmission timing ofthe SCG cell from the SeNB via the MeNB. The SeNB notifies the MeNB ofthe information about the PCH transmission timing of the SCG cell. TheMeNB notifies the UE of the information about the PCH transmissiontiming of the SCG cell. These notifications may be performed in the SeNBaddition procedure of step ST1002. A non-limiting example of theinformation about the PCH transmission timing is a DRX cycle.

The SeNB recognizes the identifier of the UE in advance. The MeNB maynotify the SeNB of the identifier of the UE that is to be subjected toDC. This notification may be made in the SeNB addition procedure of stepST1002.

The identifier of the UE may be an international mobile subscriberidentity (IMSI). The reception of the IMSI of the UE, which is to besubjected to DC, by the SeNB enables a timing at which the PCH istransmitted to the UE to be derived as in the conventional method ofderiving a timing at which the PCH is transmitted to the UE being servedby the SeNB. Also, the UE during DC can derive a timing at which the PCHis transmitted from the SCG cell by the conventional deriving method,based on its own IMSI.

In step ST1004, a cell broadcast centre (CBC) receives a PWS messagefrom a cell broadcast entity (CBE, not shown). Specifically, the CBCreceives an emergency broadcast request message as the PWS message.

In step ST1005, the CBC that has received the PWS message from the CBEnotifies the MME of the PWS message by an SBc interface.

In step ST1005, the CBC notifies the MME of the PWS message, as well asa tracking area ID list, warning area information, and a global eNB ID.The CBC may notify the identifier specific to the PWS message. Thewarning area information contains a list of cell identifiers, a list oftracking area identifiers, or an emergency area identifier.

A “Write-Replace Warning Request” message is used as the message fornotification of the PWS message, the tracking area ID list, warning areainformation, and global eNB ID. In other words, in step ST1005, the CBCnotifies the MME of the “Write-Replace Warning Request” message tonotify the MME of the PWS message, the tracking area ID list, thewarning area information, and the global eNB ID.

The MME that has received the PWS message specifies an eNB that is to benotified of the PWS message, from the tracking area ID list. Describedand shown here is a case where the SeNB is included in the tracking areaID list.

In step ST1006, the MME that has received the PWS message notifies theCBC of a PWS message reception confirm message. A “Write-Replace WarningConfirm” message is used as the message for notification of the PWSmessage reception confirm message.

In step ST1007, the CBC that has received the PWS message receptionconfirm message notifies the CBE of a PWS message reception responsemessage. Specifically, the CBC notifies an emergency broadcast responsemessage as the PWS message reception response message.

The MME may notify the PWS message reception confirm message of stepST1006 after transmitting the “Write-Replace Warning Request” message instep ST1008, which will be described below, or after receiving a“Write-Replace Warning Response” message in step ST1012, which will bedescribed below. The MME may perform this notification after notifyingthe eNB of a PWS message or receiving a response to the notification ofthe PWS message from the eNB.

In step ST1008, the MME notifies the SeNB of a PWS message by an S1-MMEinterface. In step ST1008, the MME notifies the SeNB of warning areainformation together with the PWS message. The MME may notify anidentifier specific to the PWS message. The “Write-Replace WarningRequest” message is used as the message for notification of the PWSmessage and the warning area information.

The SeNB that has received the PWS message uses the warning areainformation to confirm whether the PWS message is for the SeNB. If thePWS message is for the SeNB, the SeNB uses the warning area informationto specify a SCG cell to which the SeNB transmits a PWS message.

In step ST1009, the SeNB notifies the UE being served thereby of apaging message including a PWS indication from the specified SCG cell.The SeNB also notifies the UE during DC of the paging message includinga PWS indication. The SeNB uses the IMSI of the UE that has beenobtained in the SeNB addition procedure of step ST1002 to determine atiming at which a paging message is transmitted to the UE during DC.

In step ST1009, the UE that has received the PCH in step ST1003 receivesthe paging message mapped to the PCH from the SCG cell to receive thePWS indication.

In step ST1010, the UE that has received the PWS indication receives theSIB1 broadcast from the SCG cell to receive the scheduling informationon the SIB including the PWS message. In step ST1011, the UE thenreceives the SIB including the PWS message in accordance with thescheduling information to receive the PWS message.

For the PWS message with a sense of urgency, for example, ETWS, the UEmay receive the PWS message immediately after receiving the PWSindication.

In step ST1012, the SeNB notifies the MME of a “Write-Replace WarningResponse” message and ends the procedures of the PWS messagenotification process.

The PWS message notification process as shown in FIG. 10 enables the UEperforming DC using the SeNB to receive a PWS message for the SeNB.

The use of the notification method (1) as the PWS indicationnotification method enables the notification of a PWS indication as inthe conventional PWS indication notification method, thus preventing theprocess in the SeNB from becoming complicated.

In the presence of a plurality of SCG cells used in DC, the UE during DCneeds to receive the PCHs of the plurality of SCG cells. In this case,an amount of the PCH reception procedures by the UE during DC increases,resulting in increased power consumption. To avoid such a situation,only the SPCell may be notified of the PWS indication. Also, only theSPCell may be notified of the PWS message. An increase in the powerconsumption of the UE during DC can thus be prevented.

When the SeNB receives a PWS message from the MME, a SCG cell that isregarded as a SPCell by the UE performing DC using the SeNB may transmita PWS indication to the UE. The SPCell may transmit to the UE a PWSindication, as well as the information indicating for which SCG cell aPWS message has occurred. The UE performing DC using the SeNB mayaccordingly need to receive at least only the PCH of the SPCell.Alternatively, a PWS message may be transmitted by the SCG cell that isregarded as a SPCell by the UE performing DC using the SeNB. The UEperforming DC using the SeNB may accordingly need to receive a PWSmessage from the SPCell alone. An increase in the power consumption ofthe UE during DC can thus be prevented.

The case where the notification method (2) is applied as the PWSindication notification method will be described with reference to FIG.9 described above. The SeNB 104 that has received the PWS message fromthe MME 102 notifies the UE 105 performing DC using its own SCG cell ofa PWS indication via the MeNB 103.

More specifically, the SeNB 104 specifies a SCG cell to which the SeNB104 transmits a PWS message and notifies the UE 105 performing DC usingthe SCG cell of a PWS indication via the MeNB 103 as indicated by thearrow 109.

Upon receipt of the PWS indication transmitted from the MeNB 103, the UE105 performing DC using the SCG cell receives the SIB including the PWSmessage of the SCG cell.

FIG. 11 shows another example of the sequence of the PWS messagenotification process in the communication system of the firstembodiment. FIG. 11 shows an example of the case where the notificationmethod (2) described above is applied as the PWS indication notificationmethod. The sequence shown in FIG. 11 is similar to the sequence shownin FIG. 10, and thus, the same steps will be denoted by the same stepnumbers, and common description will be omitted.

As in the case shown in FIG. 10 described above, first, the proceduresof steps ST1001 and ST1002, and ST1004 to ST1008 are performed. The SeNBthat has received the PWS message in step ST1008 uses warning areainformation to confirm whether the received PWS message is for the SeNB.If the received PWS message is for the SeNB, the SeNB uses the warningarea information to specify a SCG cell to which the SeNB transmits thePWS message.

In step ST1101, the SeNB notifies the MeNB performing DC using thespecified SCG cell of a PWS indication. The PWS indication is notifiedby the X2 interface. Alternatively, if a new Xn interface is providedbetween the MeNB and the SeNB for DC, a notification may be made by theXn interface. The PWS indication may be included in a new messageprovided as an X2 message and notified. Alternatively, the PWSindication may be included in a message for changing the configurationof a SCG cell and notified. Still alternatively, a container for an RRCmessage may be provided in an X2 message or an Xn message, and the PWSindication may be included in the container and notified. These messagesmay be notified through dedicated signaling.

In step ST1101, the SeNB notifies the MeNB of the PWS indication, aswell as the identifier of the SeNB or the identifier of the specifiedSCG cell. In the case of recognizing the identifier of the UE during DCwith the specified SCG cell, the SeNB may notify the identifier of theUE during DC. As the method in which the SeNB recognizes the identifierof the UE during DC with the SCG cell, in the SeNB addition procedure ofstep ST1002, the MeNB may notify the SeNB of the identifier of the UEduring DC with the SCG cell.

In step ST1102, the MeNB that has received the PWS indication to the UEduring DC from the SeNB in step ST1101 notifies the UE performing DCusing the SeNB of the PWS indication. An RRC message may be used in thenotification of the PWS indication. The RRC message may be notifiedthrough dedicated signaling.

In step ST1102, the MeNB may notify the UE performing DC using the SeNBof the identifier of the PWS indication, as well as the identifier ofthe SCG cell to which the MeNB transmits a PWS message.

When being notified of the PWS indication in the container for the RRCmessage by the SeNB, the MeNB may transfer the PWS indication to an RRCmessage and dedicatedly notify the UE during DC of the container.

The MeNB that has received the PWS indication to the UE during DC fromthe SeNB in step ST1101 may use the identifier of the specified SCG cellor the identifier of the UE during DC with the specified SCG cell tonotify only the UE during DC with the specified SCG cell of the PWSindication. The PWS indication, as well as the identifier of thespecified SCG cell does not need to be notified. The UE performing DCwith the SCG cell to which the MeNB transmits no PWS message does notneed to be notified of the PWS indication. This results in a reducedsignaling load and simplified control.

Although it has been disclosed that the SeNB notifies the MeNBperforming DC using the specified SCG cell in step ST1101, the SeNB maynotify an eNB capable of DC using its own cell or a neighboring eNB ofthe PWS indication. In this case, the SeNB notifies the PWS indication,as well as the identifier of the SeNB or the identifier of the specifiedSCG cell. The eNB that has been notified of the PWS indication uses theidentifier of the SeNB or the identifier of the specified SCG cell tojudge whether the eNB is performing DC using the SeNB or the SCG cell.During DC using the SeNB or the SCG cell, the SeNB may notify the UEduring DC of the PWS indication.

In another method of notifying the UE of a PWS indication, the MeNB mayinclude a PWS indication in a paging message to be mapped to the PCH andnotify the paging message. A PWS indication of the PWS message for theSeNB during DC may be provided on the PCH. The identifier of the SCGcell that transmits a PWS message may be included together with the PWSindication. This allows the UE to specify a SCG cell that transmits aPWS message.

The MeNB may map a paging message to a PCH of the MCG cell from whichthe UE can receive the PCH.

The MeNB may map a paging message to the PCH of the PCell. This methodis applicable to the case where the UE has received the PCH of only thePCell of the MeNB.

In step ST1102, the UE that has received the PWS indication from theMeNB receives the identifier of the SCG cell that has been notifiedtogether with the PWS indication and recognizes for which SCG cell thePWS message has been transmitted.

In step ST1010, the UE that has received the PWS indication receives theSIB1 broadcast from the SCG cell to receive scheduling information onthe SIB including the PWS message. In step ST1011, the UE then receivesthe SIB including the PWS message in accordance with the schedulinginformation to receive the PWS message.

For a PWS message with a sense of urgency, for example, ETWS, the UE mayreceive a PWS message immediately after receiving a PWS indication.

In step ST1012, the SeNB notifies the MME of a “Write-Replace WarningResponse” message and ends the procedures of the PWS messagenotification process, as in the case shown in FIG. 10 described above.

The method used in the presence of a plurality of SCG cells used in DCor the method in which a SPCell notifies a PWS indication or a PWSmessage when the SeNB receives the PWS message from the MME, which hasbeen disclosed in the PWS indication notification method (1), may beapplied as the PWS indication notification method (2). This simplifiesthe PWS indication reception procedure or the PWS message receptionprocedure by the UE, resulting in reduced power consumption of the UE.

The PWS message notification process as shown in FIG. 11 above enablesthe UE performing DC using the SeNB to receive a PWS message for theSeNB.

The use of the notification method (2) above as the PWS indicationnotification method eliminates the need for the UE during DC to receivethe PCH of the SCG cell, which is required in the notification method(1) described above. The power consumption of the UE can thus bereduced.

First Modification of First Embodiment

This modification will disclose another method in which the SeNBtransmits a PWS message for the SeNB to the UE during DC.

The SeNB transmits a PWS message for the SeNB to the UE during DC viathe MeNB. The UE during DC receives the PWS message for the SeNB fromthe MeNB.

When the PWS message is notified to a specific SCG cell or specific SCGcells, the SeNB used in DC transmits a PWS message for its own SCG cellto the UE performing DC using its own SCG cell via the MeNB. The UEperforming DC using the SCG cell receives the PWS message for the SCGcell from the MeNB.

The PWS message notification method will be described. FIG. 12 shows anexample flow of a PWS message in a communication system of a firstmodification of the first embodiment. The configuration shown in FIG. 12is similar to the configuration shown in FIG. 9, and thus, the sameportions will be denoted by the same references, and common descriptionwill be omitted. With reference to FIG. 12, the flow of the PWS messageis indicated by the bold arrows 106, 107, 121, and 122.

The PWS message is notified to the CBC 101 by the CBE (not shown). TheCBC 101 notifies the MME 102 of the PWS message as indicated by thearrow 106.

The MME 102 notifies the eNB of the PWS message. Specifically, the MME102 notifies the SeNB 104 of the PWS message as indicated by the arrow107. The MME 102 also notifies the MeNB 103 of the PWS message. When itsown cell is used in DC, that is, when the eNB is the SeNB 104, the eNB104 notifies the UE 105 performing DC using its own cell of the PWSmessage via the MeNB 103, as indicated by an arrow 121 and the arrow122.

The SeNB 104 that has received the PWS message from the MME 102 notifiesthe MeNB 103 performing DC using the SeNB of the PWS message. The SeNB104 specifies a SCG cell to which the SeNB 104 transmits the PWS messageand notifies the MeNB 103 performing DC using the SCG cell of the PWSmessage.

The X2 interface 112 is used in the notification of the PWS message.Alternatively, if a new Xn interface is provided between the MeNB 103and the SeNB 104 for DC, the PWS message may be notified by means of theXn interface. The PWS message may be included in a new message providedas the X2 message and notified. Alternatively, the PWS message may beincluded in a message for changing the configuration of the SCG cell andnotified. A container for an RRC message may be provided in an X2message or an Xn message, and the PWS message may be included in thecontainer and notified. These messages may be notified through dedicatedsignaling.

The SeNB may notify the PWS message, as well as the identifier of theSeNB or the identifier of the specified SCG cell. Alternatively, whenrecognizing the identifier of the UE during DC with the specified SCGcell, the SeNB may notify the identifier of the UE during DC. The SeNBmay notify the identifier specific to the PWS message.

The MeNB that has received the PWS message from the SeNB notifies the UEperforming DC using the SeNB of the PWS message. The MeNB may notify thePWS message, as well as the identifier specific to the PWS message. TheUE performing DC using the SeNB receives the PWS message for the SeNBnotified by the MeNB. The MeNB may receive the PWS message, as well asthe identifier specific to the PWS message. This enables the UEperforming DC using the SeNB to obtain the PWS message for the SeNB.

The PWS indication may be provided to be notified to the UE during DCbefore the PWS message, as in the first embodiment. In this case, uponreceipt of the PWS indication, the UE during DC receives the PWS messagefor the SeNB notified by the MeNB.

With reference to FIG. 12, the flow of the PWS indication is indicatedby the arrows 109 and 110 and an arrow 123.

When receiving the PWS message for the SeNB from the MME 102, the SeNB104 notifies the UE 105 of the PWS indication as indicated by the arrow110. Alternatively, when the MeNB 103 receives the PWS message from theSeNB 104, the MeNB 103 may notify the UE 105 during DC of the PWSindication, as indicated by the arrow 123.

The following three, (1) to (3), will be disclosed as specific examplesof the PWS indication notification method.

(1) The SeNB 104 directly notifies the UE 105 during DC as indicated bythe arrow 110.

(2) The SeNB 104 notifies the UE 105 during DC via the MeNB 103 asindicated by the arrow 109.

(3) The MeNB 103 notifies the UE 105 during DC as indicated by the arrow123.

The method described in the first embodiment is applicable as thenotification methods (1) and (2) described above. The notificationmethod (3) described above will be described as the PWS indicationnotification method. The MeNB 103 that has received the PWS message fromthe SeNB 104 notifies the UE 105 during DC of the PWS indication. Morespecifically, the MeNB 103 uses the information indicating to which SCGcell the PWS indication is directed, which has been received togetherwith the PWS message, for example, the identifier of the SCG cell tonotify the UE 105 performing DC using the SCG cell of the PWSindication. Upon receipt of the PWS indication transmitted from the MeNB103, the UE 105 performing DC using the SCG cell receives the PWSmessage of the SCG cell from the MeNB 103.

FIG. 13 shows an example of the sequence of a PWS message notificationprocess in the communication system of the first modification of thefirst embodiment. FIG. 13 shows an example of the case where thenotification method (3) described above is applied as the PWS indicationnotification method. The sequence shown in FIG. 13 is similar to thesequences shown in FIGS. 10 and 11, and thus, the same steps will bedenoted by the same step numbers, and common description will beomitted.

First, as in the cases shown in FIGS. 10 and 11 described above, theprocedures of steps ST1001 and ST1002, and ST1004 to ST1008 areperformed. The SeNB that has received the PWS message in step ST1008uses the warning area information to confirm whether the PWS message isfor the SeNB. If the PWS message is for the SeNB, the SeNB uses thewarning area information to specify a SCG cell to which the SeNBtransmits the PWS message.

In step ST1301, the SeNB notifies the MeNB performing DC using thespecified SCG cell of the PWS message. The SeNB may notify theidentifier specific to the PWS message.

In step ST1302, the MeNB that has received the PWS message from the SeNBnotifies the UE performing DC using the SeNB of a PWS indication. TheMeNB may use an RRC message in this notification. The RRC message may benotified through dedicated signaling.

Although it has been disclosed that the SeNB notifies the MeNBperforming DC using the specified SCG cell of the PWS message in stepST1301, the SeNB may notify an eNB capable of DC using its own cell or aneighboring eNB of the PWS message. In this case, the SeNB notifies thePWS message, as well as the identifier of the SeNB or the identifier ofthe specified SCG cell. The eNB that has been notified of the PWSmessage uses the identifier of the SeNB or the identifier of thespecified SCG cell to judge whether the eNB is performing DC using theSeNB or the SCG cell. During DC using the SeNB or the SCG cell, the eNBmay notify the UE during DC of the PWS indication.

In step ST1302, the MeNB may notify the UE during DC using the SeNB ofthe PWS indication, as well as the identifier of the SCG cell to whichthe MeNB transmits the PWS message.

In another method of notifying the UE of a PWS indication, the MeNB mayinclude the PWS indication in the paging message to be mapped to the PCHand notify the UE of the paging message. The PWS indication of the PWSmessage for the SeNB during DC may be provided on the PCH. Theidentifier of the SCG cell to which the MeNB transmits the PWS messagemay be included together with the PWS indication. This allows the UE tospecify a SCG cell to which the MeNB transmits a PWS message.

The MeNB may map a paging message to the PCH of the MCG cell from whichthe UE can receive the PCH. Alternatively, the MeNB may map a pagingmessage to the PCH of the PCell. This method is applicable to the casewhere the UE has received only the PCH of the PCell of the MeNB. In thiscase, the UE is required to receive only the PCH of the PCell and is notrequired to receive the PCH transmitted from another MCG cell. Thisreduces the power consumption of the UE.

In step ST1304, the MeNB that has received the PWS message from the SeNBbroadcasts the PWS message. The MeNB includes the PWS message in the SIBand broadcasts the SIB. The SIB including the PWS message may be a newlyprovided SIB or a newly provided SIB for PWS message directed to theSeNB. Alternatively, an existing SIB may be used. Examples of theexisting SIB including the PWS message include SIB10 and SIB11 for ETWSand SIB12 for CMAS. The method in which the MeNB broadcasts the PWSmessage to the UE being served thereby is applicable as the method inwhich the MeNB notifies the UE during DC of the PWS message.

The MeNB may broadcast the PWS message for the SeNB to the UE during DCfrom the PCell. Alternatively, the MeNB may include the PWS message inthe SIB of the PCell and broadcast the SIB.

The UE during DC may receive the PWS message for the SeNB transmittedfrom the PCell.

The UE is required to receive only the SIB of the PCell and is notrequired to receive the SIB transmitted from another MCG cell. This canreduce the power consumption of the UE.

In step ST1303, the UE that has received the PWS indication from theMeNB in step ST1302 receives the SIB1 broadcast from the MeNB to receivethe scheduling information on the SIB including the PWS message. In stepST1304, the UE then receives the SIB including the PWS message inaccordance with the scheduling information to receive the PWS message.

For a PWS message with a sense of urgency, for example, ETWS, the UE mayreceive the PWS message immediately after receiving the PWS indication.

The MeNB notifies the UE during DC of the PWS indication or the PWSmessage from the PCell, thus eliminating the need for the UE to receivethe PWS indication or the PWS message from the SeNB. This reduces thepower consumption of the UE.

In step ST1012, the SeNB notifies the MME of the “Write-Replace WarningResponse” message and ends the procedures of the PWS messagenotification process, as in the cases shown in FIGS. 10 and 11 describedabove.

In the method described above, the MeNB notifies the UE during DC of theSIB including the PWS message. In another method, the MeNB may notifythe UE during DC of the RRC message including the PWS message. In thiscase, the RRC message may be notified through dedicated signaling.

When being notified of the PWS message in the container for the RRCmessage by the SeNB, the MeNB may transfer the PWS message to the RRCmessage and dedicatedly notify the UE during DC of the container.

The MeNB may notify the UE performing DC using the SeNB of the PWSmessage, as well as the identifier of the SCG cell to which the MeNBtransmits the PWS message.

The MeNB transmits the RRC message including the PWS indication and thentransmits the RRC message including the PWS message.

The MeNB may notify the UE during DC of one RRC message including thePWS indication and the PWS message. In this case, only one message isnotified, thus reducing a signaling amount between the MeNB and the UE.

The PWS message notification process as shown in FIG. 13 enables the UEperforming DC using the SeNB to receive a PWS message for the SeNB.

The MeNB notifies the UE during DC of the PWS message, thus eliminatingthe need for the UE to receive the PWS message transmitted from theSeNB. This can prevent the PWS message reception procedure from becomingcomplicated.

The UE also does not need to receive the broadcast information from theSeNB, thus reducing the power consumption of the UE.

In the PWS indication notification methods (2) and (3) described above,the MeNB notifies the UE during DC of the PWS indication. Thiseliminates the need for the UE to receive the PWS indication transmittedfrom the SeNB. The PWS message reception procedure can thus be preventedfrom becoming complicated. The UE does not need to receive the PCH ofthe SeNB, thus reducing the power consumption of the UE.

Although the example shown in FIG. 13 discloses the method of notifyingthe UE during DC of the PWS indication before the PWS message, anothermethod will be disclosed below.

In the other method, the PWS indication to the UE during DC iseliminated. In other words, the UE during DC is notified of the PWSmessage alone.

FIG. 14 shows another example of the sequence of the PWS messagenotification process in the communication system of the firstmodification of the first embodiment. FIG. 14 shows the example of thecase where the UE during DC is notified of the PWS message alone. Thesequence shown in FIG. 14 is similar to the sequences shown in FIGS. 10,11, and 13 described above, and thus, the same steps will be denoted bythe same step numbers, and common description will be omitted.

First, the procedures of steps ST1001 and step ST1002, and ST1004 tostep ST1008 are performed as in the cases shown in FIGS. 10 and 11described above. In step ST1401, the MeNB that has received the PWSmessage from the SeNB in step ST1301 notifies the UE performing DC usingthe SeNB of a PWS message. Specifically, the MeNB includes the PWSmessage in an RRC message and notifies the UE of the RRC message. TheRRC message may be notified through UE-dedicated signaling.

When being notified of the PWS message in the container for the RRCmessage by the SeNB, the MeNB may transfer the PWS message to the RRCmessage and then dedicatedly notify the UE during DC of the container.

The MeNB may notify the UE during DC using the SeNB of the identifier ofthe PWS message, as well as the identifier of the SCG cell to which theMeNB transmits the PWS message.

In step ST1401, the UE during DC receives the RRC message directed tothe UE to receive a PWS message for the SeNB.

In this manner, the MeNB notifies the UE during DC of the UE-dedicatedRRC message including the PWS message for the SeNB. As a result, theMeNB can notify a specific UE of the PWS message for the SeNB. The MeNBcan thus notify the UE of the PWS message without notifying the UE ofthe PWS indication.

As a result, the PWS indication transmission and reception proceduresare not required, thus preventing the process from becoming complicatedas a system. Signaling for PWS indication is not also required, thusreducing a signaling load.

Second Modification of First Embodiment

This modification will disclose a method in which the MeNB transmits thePWS message for the SeNB to the UE during DC.

This modification will disclose a case where the MME also notifies theMeNB of the PWS message for the SeNB. A non-limiting example of the casewhere the MME also notifies the MeNB of the PWS message for the SeNB isthe case where the MeNB and the SeNB are in the same tracking area.

The MeNB that has received the PWS message from the MME hasconventionally notified the UE being served thereby of the PWS messageonly when the PWS message is for the MeNB. If the PWS message notifiedby the MME is not for the MeNB, thus, the UE being served by the MeNB isnot notified of the PWS message.

Even when the MME also notifies the MeNB of a PWS message for the SeNB,the MeNB does not notify the UE being served thereby of the PWS message.In other words, the MeNB does not notify the UE being served thereby,which is during DC using the SeNB, of the PWS message for the SeNB.

The UE may thus fail to receive the PWS message for the SeNB. Thismodification will disclose the method of solving such a problem.

The MeNB transmits the PWS message for the SeNB to the UE during DC.

The MeNB that has received the PWS message for the SeNB from the MMEnotifies the UE during DC using the SeNB of the PWS message for theSeNB.

The PWS message notification method will be described. FIG. 15 shows anexample flow of the PWS message in a communication system of a secondmodification of the first embodiment. The configuration shown in FIG. 15is similar to the configurations shown in FIGS. 9 and 12, and thus, thesame portions will be denoted by the same references, and commondescription will be omitted. With reference to FIG. 15, the flow of thePWS message is indicated by the bold arrow 106 and bold arrows 151 and152.

As indicated by the arrow 151, the MME 102 that has received the PWSmessage from the CBC 101 notifies not only the SeNB 104 but also theMeNB 103 of the PWS message.

The MeNB 103 judges whether the PWS message received from the MME 102 isfor the SeNB 104 used in DC. When receiving the PWS message for the SeNB104 used in DC, as indicated by the arrow 152, the MeNB 103 notifies theUE 105 performing DC using the SeNB 104 of the PWS message.

As indicated by the arrow 152, the UE 105 performing DC using the SeNB104 receives the PWS message for the SeNB 104 from the MeNB 103.

As indicated by the arrow 152, the UE 105 performing DC using the SeNB104 can accordingly obtain the PWS message for the SeNB.

The PWS indication may be provided also in this modification to benotified to the UE during DC before the PWS message, as in the firstmodification of the first embodiment. Upon receipt of the PWSindication, the UE during DC receives the PWS message for the SeNBnotified by the MeNB.

FIG. 15 also shows the flow of the PWS indication. With reference toFIG. 15, the flow of the PWS indication is indicated by the thin arrow123.

When the MeNB 103 receives the PWS message for the SeNB 104 used in DCfrom the MME 102 as indicated by the arrow 151, as indicated by thearrow 123, the MeNB 103 may notify the UE 105 performing DC using theSeNB 104 of the PWS indication.

The PWS indication notification method (3) disclosed in the firstmodification of the first embodiment is applicable as the PWS indicationnotification method.

FIG. 16 shows an example of the sequence of the PWS message notificationprocess in the communication system of the second modification of thefirst embodiment. FIG. 16 shows the example of the case where the PWSindication notification method (3), which has been disclosed in thefirst modification of the first embodiment, is applied as the PWSindication notification method. The sequence shown in FIG. 16 is similarto the sequences shown in FIGS. 10, 11, and 13 described above, andthus, the same steps will be denoted by the same step numbers, andcommon description will be omitted.

First, the procedures of steps ST1001, ST1002, ST1004, and ST1005 areperformed as in the cases shown in FIGS. 10 and 11 described above. TheMME that has received the PWS message from the CBC in step ST1005specifies an eNB that is to be notified of the PWS message, from thetracking area ID list notified together with the PWS message. Describedhere is the case where the tracking area ID list includes the MeNB andthe SeNB.

In step ST1008, the MME uses the S1-MME interface to notify the SeNB ofthe PWS message. In step ST1601, the MME also uses the S1-MME interfaceto notify the MeNB of the PWS message. Specifically, the MME notifiesthe PWS message, as well as the warning area information. The“Write-Replace Warning Request” message is used as the message fornotification of the PWS message and the warning area information.

In step ST1602, the MeNB that has received the PWS message in stepST1601 uses the warning area information to judge whether the PWSmessage is for the SeNB used in DC.

If the PWS message is not for the SeNB used in DC, the MeNB returns tothe normal process without performing the procedure for transmitting thePWS message to the UE performing DC using the SeNB. If the PWS messageis for the SeNB used in DC, the MeNB uses the warning area informationto specify a SCG cell to which the MeNB transmits the PWS message.

In step ST1302, the MeNB notifies the UE performing DC using the SeNB ofthe PWS indication.

The UE during DC that has received the PWS indication receives the PWSmessage notified by the MeNB through the procedures of steps ST1303 andST1304. The method of the first modification of the first embodiment isapplicable as the methods for the procedures of steps ST1303 and ST1304,and thus, description thereof will be omitted here.

In step ST1603, the MeNB notifies the MME of the “Write-Replace WarningResponse” message and then ends the procedures of the PWS messagenotification process.

The PWS message notification process as shown in FIG. 16 above enablesthe UE performing DC using the SeNB to receive a PWS message for theSeNB.

The MeNB does not need to receive the PWS message from the SeNB, thusreducing the PWS message transmission and reception procedures betweenthe SeNB and the MeNB. The procedures by the SeNB and the MeNB canaccordingly be simplified, thus reducing the signaling load between theSeNB and the MeNB.

Although this modification has disclosed the method of notifying the UEduring DC of the PWS indication before the PWS message, another methodwill be disclosed below.

The PWS indication to the UE during DC is eliminated. In other words,the UE during DC is notified of the PWS message alone.

FIG. 17 shows another example of the sequence of the PWS messagenotification process in the communication system of the secondmodification of the first embodiment. FIG. 17 shows the case where theUE during DC is notified of the PWS message alone. The sequence shown inFIG. 17 is similar to the sequences shown in FIGS. 10, 11, 13, 15, and16, and thus, the same steps will be denoted by the same step numbers,and common description will be omitted.

First, the procedures of steps ST1001, ST1002, ST1004 to ST1008, andST1601 are performed as in the case shown in FIG. 16 described above. Instep ST1602, the MeNB that has received the PWS message from the MME instep ST1601 uses the warning area information to judge whether the PWSmessage is for the SeNB used in DC.

If the PWS message is not for the SeNB used in DC, the MeNB returns tothe normal process without performing the procedure of transmitting thePWS message to the UE performing DC using the SeNB. If the PWS messageis for the SeNB used in DC, the MeNB uses the warning area informationto specify a SCG cell to which the MeNB transmits the PWS message.

In step ST1401, the MeNB notifies the UE performing DC using the SeNB ofthe PWS message. Specifically, the MeNB includes the PWS message in theRRC message and notifies the RRC message. The RRC message may benotified through UE-dedicated signaling.

The MeNB may notify the UE performing DC using the SeNB of the PWSmessage, as well as the identifier of the SCG cell to which the MeNBtransmits the PWS message.

In step ST1401, the UE during DC receives the RRC message directed tothe UE to receive the PWS message for the SeNB.

As described above, the MeNB notifies the UE during DC of theUE-dedicated RRC message including the PWS message for the SeNB, thusnotifying a specific UE of the PWS message for the SeNB. The MeNB canthus notify the UE of the PWS message without notifying the UE of thePWS indication.

As a result, the PWS indication transmission and reception proceduresare not required, thus preventing the process from becoming complicatedas a system. Signaling for PWS indication is not also required, thusreducing a signaling load.

Third Modification of First Embodiment

This modification will disclose another method in which the MeNBtransmits a PWS message for the SeNB to the UE during DC.

The second modification of the first embodiment has disclosed the casewhere the MME also notifies the MeNB of a PWS message for the SeNB. Insome cases, however, the MME does not notify the MeNB of a PWS messagefor the SeNB. A non-limiting example of the case above is the case wherethe MeNB and the SeNB are in different tracking areas. In such a case,the method disclosed in the second modification of the first embodimentis not applicable.

This modification will disclose the method of solving such a problem.

The MeNB notifies the MME of the information about the SeNB used in DC.The MeNB may provide this notification in changing the SeNB or the SCGcell used in DC. The information about the SeNB possessed by the MME isaccordingly updated as appropriate. The information about the SeNB usedin DC may be notified in the SeNB addition procedure. Alternatively, theinformation may be notified in the SeNB change procedure or the SeNBmodification procedure. In the SeNB release procedure, the MeNB maynotify the MME of the information indicating that no SeNB is used in DC.

The MME can accordingly associate the SeNB to which the MME transmitsthe PWS message and the MeNB using the SeNB in DC with each other. TheMME can thus notify the MeNB using the SeNB in DC of the PWS message forthe SeNB.

When receiving the PWS message, the MME judges whether the PWS messageis for the SeNB used in DC. When receiving the PWS message for the SeNBused in DC, the MME notifies the MeNB of the PWS message.

The MeNB judges whether the PWS message received from the MME is for theSeNB used in DC. When receiving the PWS message for the SeNB used in DC,the MeNB notifies the UE performing DC using the SeNB of the PWSmessage.

The UE performing DC using the SeNB cell receives a PWS message for theSeNB cell from the MeNB.

The PWS message notification method will be described. The flow of thePWS message in this modification is similar to the flow in the case ofthe second modification of the first embodiment shown in FIG. 15described above.

As in the second modification of the first embodiment, a PWS indicationmay be provided to be notified to the UE during DC before the PWSmessage. Upon receipt of the PWS indication, the UE during DC receivesthe PWS message for the SeNB notified by the MeNB.

The flow of the PWS indication in this modification is similar to theflow in the case of the second modification of the first embodimentshown in FIG. 15 described above.

When the MeNB receives the PWS message for the SeNB used in DC from theMME, the MeNB may notify the UE performing DC using the SeNB of the PWSindication. The PWS indication notification method (3) disclosed in thefirst modification of the first embodiment is applicable as the PWSindication notification method.

FIG. 18 shows an example of the sequence of the PWS message notificationprocess in a communication system of a third modification of the firstembodiment. The sequence shown in FIG. 18 is similar to the sequenceshown in FIG. 16 described above, and thus, the same steps will bedenoted by the same step numbers, and common description will beomitted.

First, the procedure of step ST1001 is performed as in the case shown inFIG. 16 described above. In step ST1002, the MeNB activates the SeNBaddition procedure to perform DC to the UE. The SeNB addition procedureis accordingly performed among the MeNB, the UE, and the SeNB. In theSeNB addition procedure, the SeNB notifies the MeNB of the cell ID ofits own cell, TAI, or emergency area ID.

In step ST1801, the MeNB notifies the MME of the information about theadded SeNB. Alternatively, the MeNB may notify the information about theSCG cell. The information about the SeNB may be the information by whichthe warning area information can be specified, specifically, the cell IDof the SeNB, TAI, or emergency area ID. The MeNB may notify theidentifier of the MeNB performing DC using the SeNB as the informationabout the SeNB. As a result, the information about the SeNB is theinformation about the SeNB used in DC by which MeNB can be recognized.

If the DC using the SeNB is DC architecture 1A, the MeNB notifies theMME of a path change of a user plane (U-plane) in the S-GW in the SeNBaddition procedure for the execution of DC in step ST1002. The MeNB mayuse this change notification to notify the information about the addedSeNB. For example, the MeNB may include the information about the SeNBin a path change notification message and then notify the MME of themessage. Alternatively, the MeNB may notify the MME of another messageincluding the information about the SeNB in the SeNB addition procedure.

The MME that has received the PWS message from the CBC in step ST1005specifies an eNB that is to be notified of the PWS message, from thetracking area ID list received together with the PWS message.

In step ST1802, the MME uses the specified eNB and the information aboutthe added SeNB, which has been received from the MeNB in step ST1801, tojudge whether the eNB is the SeNB during DC. If the specified eNB is theSeNB during DC, the MME judges that the PWS message is for the SeNBduring DC. If the specified eNB is not the SeNB during DC, the MMEjudges that the PWS message is not for the SeNB during DC.

If the PWS message is not for the SeNB during DC, the MME may return tothe normal process without performing the PWS message transmissionprocedure to the MeNB performing DC using the SeNB.

If the PWS message is for the SeNB during DC, the MME uses theinformation about the added SeNB, which has been received from the MeNBin step ST1801, to specify an eNB to which the MME transmits the PWSmessage. The eNB is the MeNB herein. The MME may associate theinformation about the added SeNB, which has been received in stepST1801, and the MeNB, which has notified of the information, with eachother to specify an eNB to which the MME transmits the PWS message usingthe MeNB information associated with the SeNB.

The MME that has specified an eNB to which the MME transmits the PWSmessage notifies the eNB of the PWS message. The eNB is the MeNB herein.In step ST1601, the MME also notifies the MeNB of the PWS message forthe SeNB by the S1-MME interface.

The MME notifies the PWS message, as well as a tracking area ID list,warning area information, and global eNB ID. The “Write-Replace WarningRequest” message is used as the message for the notification.Alternatively, the identifier specific to a PWS message may be notified.

In step ST1602, the MeNB that has received the PWS message in stepST1601 uses the warning area information to judge whether the PWSmessage is for the SeNB used in DC.

If the PWS message is not for the SeNB used in DC, the MeNB returns tothe normal process without performing the procedure for transmitting aPWS message to the UE performing DC using the SeNB. If the PWS messageis for the SeNB used in DC, the MeNB uses the warning area informationto specify a SCG cell to which the MeNB transmits a PWS message.

In step ST1302, the MeNB notifies the UE performing DC using the SeNB ofthe PWS indication. In steps ST1303 and ST1304, the UE during DC thathas received the PWS indication receives the PWS message notified by theMeNB. The method of the first modification of the first embodiment isapplicable as the methods of steps ST1303 and ST1304, and thus,description thereof will be omitted here.

If judging in step ST1802 that the PWS message is for the SeNB duringDC, the MME may notify the MeNB of the PWS message, as well as theinformation indicating that the PWS message is for the SeNB during DC.This enables the MeNB to explicitly recognize that the received PWSmessage is for the SeNB used in DC. The MeNB may use the information inthe judgment of step ST1602. This reduces malfunctions.

The PWS message notification process as shown in FIG. 18 above enablesthe UE performing DC using the SeNB to receive a PWS message for theSeNB.

If the MME does not notify the MeNB of the PWS message for the SeNB, forexample, if the MeNB and the SeNB are in different tracking areas, theMeNB can notify the UE during DC of a PWS message for the SeNB.

The UE during DC can receive the PWS message for the SeNB from the MeNB.

Although this modification has disclosed the method of notifying the UEduring DC of a PWS indication before a PWS message, another method willbe disclosed below.

The PWS indication to the UE during DC is eliminated. In other words,the UE during DC is notified of the PWS message alone.

FIG. 19 shows another example of the sequence of the PWS messagenotification process in the communication system of the thirdmodification of the first embodiment. FIG. 19 shows the case where theUE during DC is notified of a PWS message alone. The sequence shown inFIG. 19 is similar to the sequences shown in FIGS. 17 and 18, and thus,the same steps will be denoted by the same step numbers, and commondescription will be omitted.

In the example shown in FIG. 19, first, the procedures of steps ST1001,ST1002, ST1801, ST1004 to ST1008, ST1802, ST1601, and ST1602 areperformed as in the case shown in FIG. 18 described above. Subsequently,the procedures of steps ST1401, ST1012, and ST1613 are performed as inthe case shown in FIG. 17 described above.

As a result, the PWS indication transmission and reception proceduresare not required also in this modification, thus preventing the processfrom becoming complicated as a system. Also, signaling for PWSindication is not required, thus reducing a signaling load.

Fourth Modification of First Embodiment

This modification will disclose another method in which the SeNBtransmits a PWS message for the SeNB to the UE during DC.

This modification will describe the case where the MME connected to theMeNB differs from the MME connected to the SeNB.

In this case, the SeNB that has received the PWS message from the MMEmay transmit the PWS message for the SeNB to the UE during DC. The SeNBdirectly transmits the PWS message for the SeNB to the UE during DC.Alternatively, the SeNB may transmit the PWS message for the SeNB to theUE during DC via the MeNB.

The UE during DC receives a PWS message for the SeNB from the SeNB orthe MeNB. The method disclosed in the first embodiment or the firstmodification of the first embodiment is applicable as the method used insuch a case. The same applies to the case where a PWS message isnotified to a specific SCG cell or specific SCG cells.

The PWS message notification method will be described. FIG. 20 shows anexample flow of the PWS message in a communication system of a fourthmodification of the first embodiment. The configuration shown in FIG. 20is similar to the configurations shown in FIGS. 9 and 12, and thus, thesame portions will be denoted by the same references, and commondescription will be omitted. With reference to FIG. 20, the flow of thePWS message is indicated by bold arrows 202 and 203 and the bold arrows121, 122, and 108.

FIG. 20 shows the case where an MME connected to the SeNB 104(hereinbelow also referred to as “MME for SeNB”) 201 differs from theMME 102 connected to the MeNB 103 (hereinbelow also referred to as “MMEfor MeNB”).

The CBC 101 is connected to the MME for SeNB 201. With reference to FIG.20, the flow of the PWS message from the CBC 101 to the SeNB 104 isindicated by the bold arrows 202 and 203.

The PWS message is notified to the CBC 101 by the CBE (not shown), tothe MME for SeNB 201 by the CBC 101, and to the SeNB 104 by the MME forSeNB 201.

When the eNB is used in DC, that is, when the eNB is the SeNB 104, theSeNB 104 notifies the UE 105 performing DC using the SeNB of a PWSmessage as indicated by the arrow 108. In this case, the PWS indicationis also notified to the MeNB 103 and the UE 105 by the SeNB 104 asindicated by the arrows 109 and 110.

The SeNB 104 may notify the UE 105 performing DC using its own cell of aPWS message via the MeNB 103 as indicated by the arrows 121 and 122. Inthis case, the PWS indication is notified to the MeNB 103 and the UE 105by the SeNB 104 as indicated by the arrows 110, 109, and 123.

The method disclosed in the first embodiment described above isapplicable as the method of notifying of a PWS message and a PWSindication used in the case where the SeNB notifies the UE during DC ofthe PWS message. This method enables the UE performing DC using the SeNBto receive the PWS message from the SeNB.

The method disclosed in the first modification of the first embodimentdescribed above is applicable as the method of notifying of a PWSmessage and a PWS indication used in the case where the SeNB notifiesthe UE during DC of a PWS message for the SeNB via the MeNB. This methodenables the UE performing DC using the SeNB to receive the PWS messagefor the SeNB from the MeNB.

As a result, also when the MME connected to the MeNB differs from theMME connected to the SeNB, the UE performing DC using the SeNB canreceive the PWS message for the SeNB.

The method disclosed in the third modification of the first embodimentdescribed above is applicable to the case where the CBC is connectedwith the MME connected to the MeNB and the MME connected to the SeNBthough the MME connected to the MeNB differs from the MME connected tothe SeNB.

In this case, the CBC notifies the MME connected with the MeNB of thePWS message. The method disclosed in the third modification of the firstembodiment described above is applicable as the method of notifying of aPWS message for the SeNB between the MME that has been notified of thePWS message and the UE during DC.

As a result, the UE performing DC using the SeNB can receive the PWSmessage for the SeNB.

The method disclosed in the second modification of the first embodimentdescribed above is applicable to the case where the CBC is connectedwith the MME connected to the MeNB and the MME connected to the SeNBthough the MME connected to the MeNB differs from the MME connected tothe SeNB and where the MeNB and the SeNB are located in the sametracking area (TA).

The UE performing DC using the SeNB can thus receive the PWS message forthe SeNB. The same applies to the case where the MCG cell and the SCGcell are located in the same TA.

Both the MeNB and the SeNB may notify the UE being served thereby of thesame PWS message. In other words, the PWS message for the MeNB is thesame as the PWS message for the SeNB in some cases. In such a case, theuse of the methods disclosed in this embodiment and the modificationthereof enables the UE to receive the PWS message for the MeNB and thePWS message for the SeNB. In other words, the UE receives the same PWSmessage redundantly.

The UE is configured to receive the same PWS messages redundantly, andcan accordingly receive any one of the PWS messages if it fails toreceive the other PWS message. This reduces a probability that the UEwill fail to receive a PWS message. A robust system can therefore beconstructed as a PWS.

The redundant reception of the same PWS message by the UE may lead to anincrease in power consumption. The following three, (1) to (3), will bedisclosed as the method for solving this problem.

(1) In the case where the UE is notified of the PWS messages by both theMeNB and the SeNB, the UE judges whether the PWS message notified by theMeNB is the same as the PWS message notified by the SeNB. Amessage-specific identifier notified together with the PWS message maybe used in this judgment. A non-limiting example of the message-specificidentifier is a message ID. The UE receives the PWS message notifiedfirst. During the reception, the UE records the message ID of the PWSmessage. The UE compares the message ID of the PWS message notifiedlater with the message ID of the PWS message previously received.

If the message IDs are the same, the UE does not receive the PWS messagenotified later or may avoid the demodulation of the PWS message notifiedlater. If the message IDs are different, the UE receives the PWS messagenotified later and records the message ID thereof. The UE repeats theoperations above, thus preventing the redundant reception of the samePWS messages. This prevents an increase in the power consumption of theUE. The method (1) above is applicable to the case where the methoddisclosed in the first embodiment is used.

(2) In the case where the MeNB receives a PWS message from the SeNB, theMeNB may judge whether the PWS message for the MeNB is the same as thePWS message for the SeNB. The PWS indication notification method may bethe method (2) or (3) described above.

The judgment method by the MeNB will be disclosed. The MeNB records themessage ID of the PWS message for the MeNB and compares the recordedmessage ID of the PWS message for the MeNB with the message ID notifiedtogether with the PWS message received from the SeNB. If the message IDsare the same, the MeNB does not transmit the PWS message received fromthe SeNB to the UE performing DC using the SeNB. In this case, the MeNBmay avoid notifying the UE of the PWS indication as well. If the messageIDs are different, the MeNB transmits the PWS message received from theSeNB to the UE performing DC using the SeNB.

As a result, the redundant reception of the same PWS message by the UEcan be prevented. This prevents an increase in the power consumption ofthe UE.

The method (2) above is applicable to the case where the methoddisclosed in the first modification of the first embodiment is used.

(3) In the case where the MeNB receives the PWS message for the SeNBfrom the MME, the MeNB judges whether the PWS message for the MeNB isthe same as the PWS message for the SeNB.

The judgment method by the MeNB will be disclosed. The MeNB determineswhether the PWS message received from the MME is for the SeNB and forthe MeNB. In this case, the MeNB may make a judgment using the warningarea information notified together with the PWS message by the MME.Specifically, the MeNB judges whether the warning area informationincludes both the MeNB and the SeNB performing DC with the MeNB as theinformation about the eNB or the cell to which the MeNB transmits thePWS message.

If the information includes both the MeNB and the SeNB, the MeNB judgesthat the PWS message for the MeNB is the same as the PWS message for theSeNB and transmits the PWS message only once to the UE performing DCusing the SeNB. In this case, the MeNB may also notify the UE of the PWSindication only once. The MeNB may avoid performing the method ofnotifying of a PWS message for the SeNB. If the information includesneither the MeNB nor the SeNB, the MeNB notifies the UE of the PWSmessage by the respective PWS message notification methods.

In this manner, the UE can be prevented from redundantly receiving thesame PWS message. This prevents an increase in the power consumption ofthe UE.

The method (3) above is applicable to the case where the methoddisclosed in the second modification of the first embodiment is used andthe case where the method disclosed in the third modification of thefirst embodiment is used.

In the case where the method disclosed in the fourth modification of thefirst embodiment is used, the methods disclosed above may be applied asappropriate in accordance with the path for notification of the PWSmessage. Similar effects can therefore be achieved.

Second Embodiment

A problem to be solved in a second embodiment and a solution to theproblem will be described below.

The emergency service such as an emergency call may conceivably requirelarge volumes of data communications, such as map information, in thefuture. Thus, it is conceivably requested that DC be enabled to anemergency session for emergency service or an emergency bearer foremergency service.

3GPP has pursued the specification standard of the emergency service(see 4.3.12 of Non-Patent Document 13) but has discussed nothing aboutthe introduction of DC to the emergency service.

Thus, when the procedure for performing DC, such as the SeNB additionprocedure or the SeNB modification procedure under discussion of 3GPP(see (Non-Patent Document 9), is merely applied to an emergency bearer,DC using the SeNB cannot be performed to the emergency bearer in somecases.

For example, in the execution of DC to a bearer, the MeNB does notnotify the SeNB of whether the bearer is an emergency bearer whennotifying the SeNB of a SeNB addition request. The SeNB accordinglycannot recognize whether the SeNB addition request from the MeNB is foran emergency bearer.

In some cases, the SeNB rejects a SeNB addition request received fromthe MeNB, depending on the resource status of the SeNB or the SCG cell.Examples of such a case include the case where the SeNB is overloaded,the case where the SeNB is notified of the overload start procedure bythe MME, and the case where the SeNB restricts access of the UE being aDC target such as the case of “not suitable”. In such a case, the SeNBrejects a SeNB addition request from the MeNB.

The SeNB that does not recognize that the SeNB addition procedure is toan emergency bearer may reject the SeNB addition procedure depending onthe status of the SeNB. The MeNB that has been rejected cannot performDC to the emergency bearer. In other words, the MeNB cannot perform DCto the UE to which the MeNB provides an emergency service.

This embodiment will disclose the method of enabling DC to an emergencybearer. The solution in the second embodiment will be described below.

In the request for the procedure for performing DC from the MeNB, theSeNB does not reject the request if the request is a request for anemergency bearer. Examples of the request for the procedure forperforming DC include a SeNB addition request and a SeNB modificationrequest. When performing DC to the emergency bearer, the MeNB includesthe information indicating that these requests are made to an emergencybearer in the SeNB addition request or the SeNB modification request.

FIG. 21 shows an example of the sequence of a DC execution process to anemergency bearer in a communication system of the second embodiment.

Although the MeNB and the SeNB are used when DC has been performed, theeNBs, which will be used in DC later, will be denoted by the MeNB andthe SeNB for the sake of brevity.

First, description will be given of the flow of theemergency-bearer-related information in the establishment of anemergency bearer for emergency service.

In step ST2201, the UE that performs an emergency service includes theinformation indicating that an attach request or a PDN connectivityrequest is made because of an emergency (hereinbelow also referred to as“emergency information”) in the attach request or the PDN connectivityrequest as a NAS message and notifies the MME of the request. In thisembodiment, the UE includes the emergency information in a PDNconnectivity request and then notifies the MME of the request.

At that time, the UE includes the emergency information in the RRCconnectivity request message regarding an emergency service and notifiesthe MeNB of the message. For example, the UE includes the emergencyinformation in an RRC connection establishment request message as an RRCconnectivity request message and notifies the MeNB of the message.

The MeNB uses the emergency information to judge whether the request isfor an emergency service. If the request is for an emergency service,the MeNB accepts the request without access restriction that isperformed for a normal bearer.

The MeNB includes the emergency information in an initial NAS message asan S1 message and then notifies the MME of the message. The MME uses theemergency information of the initial NAS message or the emergencyinformation included in the attach request or PDN connectivity requestto judge whether such a request is for an emergency service.

If the request is for an emergency service, the MME selects a P-GW foremergency service (emergency P-GW). The MME then derives the address ofthe emergency P-GW.

In step ST2202, the MME includes the address of the emergency P-GW in acreate session request message as an S11 message and then notifies theS-GW of the message. In step ST2203, the S-GW uses the address of theemergency P-GW to notify the emergency P-GW of a create session requestas an S5 message.

In step ST2204, the emergency P-GW obtains an allocation and retentionpriority (ARP) value for emergency service from a policy and chargingrules function (PCRF).

The emergency P-GW that has obtained the ARP value for emergency serviceuses the ARP value to derive QoS-related information for EPS bearer.Examples of the QoS-related information for EPS bearer include QCI, ARP,GBR, and MBR.

In step ST2205, the emergency P-GW includes the QoS-related informationfor EPS bearer in a create session response message and then notifiesthe S-GW of the message. In step ST2206, the S-GW includes theQoS-related information for EPS bearer in the create session responsemessage and then notifies the MME of the message. The MME derivesE-UTRAN radio access bearer (E-RAB) level QoS information from thereceived QoS-related information for EPS bearer.

In step ST2207, the MME includes the E-RAB level QoS information and theARP value in an E-RAB setup request message and notifies the MeNB of themessage. The S1 message is used in this notification. The MeNB performsa configuration for the E-RAB provided between the S-GW and the UE viathe MeNB, based on the received E-RAB level QoS information.

In step ST2208, the MeNB includes a resource configuration for E-RAB inan RRC connection reconfiguration message based on the received E-RABlevel QoS information and notifies the UE of the message.

The MME includes the QoS-related information for EPS bearer except forARP in an attach response message or a PDN connectivity accept messageand notifies the UE of the message. The accept response message or thePDN connectivity accept message may be an activate dedicated EPS bearercontext request message.

The UE that has received the resource configuration for E-RAB throughthe RRC connection reconfiguration message performs a resourceconfiguration for E-RAB, and in step ST2209, notifies the MeNB of an RRCconnection reconfiguration complete message.

In step ST2210, the MeNB that has performed the configuration for E-RABnotifies the MME of a bearer setup response message.

The UE that has received the attach response message or the PDNconnectivity accept message, which is a NAS message, notifies the MME ofthe completion of PDN connectivity through a direct transfer message instep ST2211 and a PDN connectivity complete message in step ST2212.

In step ST2213, a path configuration procedure is performed. As aresult, an emergency bearer is configured, thus enabling UL/DL datacommunications to the emergency bearer as indicated by step ST2214.

The conventional method of performing DC will be described beforedisclosing the method of performing DC in an emergency bearer.

The MeNB that has determined to perform DC to the UE requests resourcesfrom the SeNB such that a total of the resource provided to the UE bythe MeNB and the resource provided to the UE by the SeNB ensures theE-RAB level QoS requested from the MME.

The MeNB thus may configure a value, which is different from that of theE-RAB level QoS information requested from the MME, to the SeNB. TheMeNB includes the E-RAB level QoS information requested for the SeNB ina DC execution request message to the SeNB, for example, SeNB additionrequest message, and notifies the SeNB of the message (see Non-PatentDocument 9).

The SeNB addition request in the execution of DC that is underdiscussion of 3GPP is as described above.

In this method, however, the SeNB cannot recognize whether the bearer towhich the execution of DC is requested by the MeNB is for an emergencyservice. This is because the MeNB configures a resource request to theSeNB, and accordingly, whether the MeNB includes an ARP value in the DCexecution request message is not explicit. This is also because evenwhen a DC execution request message including an APR value is made, theARP may not have an ARP value for an emergency service.

As described above, the SeNB that does not recognize that the SeNBaddition procedure is to an emergency bearer rejects the proceduredepending on the status of the SeNB, and accordingly cannot perform DCto the UE to which the SeNB provides an emergency service.

The method for solving such a problem will be disclosed.

The MeNB includes the information indicating that the request is a DCexecution request to an emergency bearer in a DC execution request tothe SeNB. The SeNB that has received the DC execution request to anemergency bearer does not reject the DC execution request, that is,allows the execution of DC.

An example of the method of performing DC to an emergency bearer will bedescribed with reference to FIG. 21.

As described above, in step ST2214, the UL/DL data communications to theemergency bearer are performed. In step ST2215, the MeNB notifies theSeNB of a DC execution request message to the SeNB, for example, a SeNBaddition request message.

In this case, the information indicating that the request is made to theemergency bearer is included in the DC execution request message to theSeNB, for example, the SeNB addition request message, and is notified.The information indicating that the request is made to an emergencybearer may be included in the SeNB addition request message togetherwith the E-RAB level QoS information requested for the SeNB and may benotified. Alternatively, a new message for notifying the informationindicating that a DC execution request is made to an emergency bearermay be provided.

The MeNB may also notify the SeNB of the new message in making a DCexecution request to an emergency bearer. An X2 interface or an Xninterface may be used in the notification of the information.Alternatively, the information may be an indication or causeinformation.

The SeNB can accordingly recognize that the request is a DC executionrequest message to an emergency bearer. The SeNB that has received theinformation indicating that the request is made to an emergency bearerin step ST2215 uses this information to judge whether the request is aDC execution request to an emergency bearer.

If the request is not a DC execution request to an emergency bearer, theSeNB determines whether to reject or accept the request in accordancewith the status of the SeNB or the SCG cell. If the request is a DCexecution request to an emergency bearer, the SeNB does not reject therequest, that is, accepts the request.

Since FIG. 21 shows the case where a request is a DC execution requestto an emergency bearer, the SeNB does not reject but accepts a DCexecution request.

In step ST2216, the SeNB notifies the MeNB of DC execution requestacknowledge, for example, SeNB addition request acknowledge. In stepST2217, the MeNB configures a radio resource for execution of DC to theUE through an RRC connection reconfiguration message.

In step ST2218, the UE that has configured the radio resource for DCusing the SeNB notifies the MeNB of the completion of the configurationthrough an RRC connection reconfiguration complete message.

In step ST2219, the MeNB notifies the SeNB that the configuration of aradio resource for DC using the SeNB has completed through a SeNBreconfiguration complete message. As a result, in step ST2220, a DCexecution process to an emergency bearer is performed among the MeNB,the SeNB, and the UE.

In step ST2215, the MeNB may notify the SeNB of a bearer configurationfor emergency bearer in the DC execution request message for anemergency bearer, for example, a SeNB addition request or a SeNBmodification request. In other words, the MeNB may request the bearerconfiguration identical to the bearer configuration configured to itselffrom the SeNB.

In other words, the MeNB does not configure a value, which differs froma value of the E-RAB level QoS information requested from the MME, tothe SeNB to request a resource from the SeNB for an emergency bearer.The MeNB configures the same value to the SeNB.

For example, the MeNB configures the E-RAB level QoS information for anemergency bearer, notified by the MME, to the SeNB and makes a DCexecution request. An ARP value may be included as the E-RAB level QoSinformation for an emergency bearer.

The SeNB can accordingly recognize that the request is a DC executionrequest to an emergency bearer, and thus, does not reject the DCexecution request to the emergency bearer. This eliminates the casewhere the SeNB rejects a DC execution request depending on the status ofthe SeNB or the SCG cell. The SeNB can therefore perform DC to the UE towhich the SeNB provides an emergency service.

In step ST2215, the MeNB may notify the SeNB of an ARP value indicatingthat a request is made for an emergency bearer in a DC execution requestmessage for an emergency bearer, for example, a SeNB addition request ora SeNB modification request. The SeNB may recognize an ARP value for anemergency bearer in advance. For example, an ARP value may be determinedstatically in specifications in advance or may be set by an operator.

In another method, the P-GW may obtain an ARP value for an emergencybearer from the PCRF and notify the SeNB of the ARP value via the MME.In still another method, the MME may obtain an ARP value for anemergency bearer from the P-GW and notify the SeNB of the ARP value. TheARP value may be dedicated to an emergency bearer.

As a result, the SeNB can make a judgment based on an ARP value withoutthe use of the information indicating that the request is made to anemergency bearer. This eliminates the need for the MeNB to notify theSeNB of the information, thus reducing an information amount betweenX2's or Xn's.

First Modification of Second Embodiment

The SeNB does not allow the establishment of an emergency bearer in somecases, for example, the case where a local regulation or an operator'spolicy does not permit the establishment of an emergency bearer. In sucha case, even when the MeNB shows the SeNB that the execution of DC isrequested to an emergency bearer, the SeNB cannot accept the request.

The method disclosed in the second embodiment may prevent the SeNB fromrejecting a request even in such a case.

This modification will disclose the method of solving this problem.

When the SeNB does not allow the establishment of an emergency bearer,the SeNB rejects a DC execution request from the MeNB, for example, aSeNB addition request or a SeNB modification request if the request isfor an emergency bearer. The SeNB may notify the MeNB of a rejectmessage. The message may include reject cause information. Theinformation indicating that the establishment of an emergency bearer isnot allowed may be provided as the reject cause information. If the SeNBdoes not allow the establishment of an emergency bearer, the SeNB mayinclude the information indicating that the establishment of anemergency bearer is not allowed in a reject message and notify the MeNBof the message when rejecting a DC execution request to the emergencybearer from the MeNB. The MeNB that has received the informationindicating that the establishment of an emergency bearer is not alloweddoes not perform DC to the UE using the SeNB.

The MeNB that has received the reject message can judge whether toperform DC using another SeNB. For the MeNB that has received the rejectmessage to perform DC using another SeNB, the MeNB that has received thereject message may prohibit a DC execution request to the SeNB that hasbeen notified of the reject message for a predetermined period. Thiseliminates the need for unnecessary notification of a DC executionrequest message, thus reducing a signaling amount.

A predetermined period may be determined statically in advance, forexample, may be determined in specifications. Statically determining apredetermined period can facilitate the process. Alternatively, the SeNBmay include a predetermined period in a reject message and notify theMeNB of the message. In this case, the SeNB can set a predeterminedperiod flexibly in accordance with its status. As a result, thecommunication system can be operated flexibly. The method describedabove is applicable to any reject message in addition to a rejectmessage that is provided because the establishment of an emergencybearer is not allowed.

Another method of solving the problem described in this modificationwill be disclosed.

Also in the case where the SeNB does not allow the establishment of anemergency bearer, the SeNB notifies the MeNB of a DC execution requestacknowledge message once. The information indicating that theestablishment of an emergency bearer is not allowed is included in theDC execution request acknowledge message. When receiving the informationindicating that the establishment of an emergency bearer is not allowedfrom the SeNB, the MeNB notifies the SeNB of a DC execution releasemessage, for example, a SeNB release message. The MeNB does not notifythe UE of an RRC connection reconfiguration message. The MeNBaccordingly does not use the SeNB in DC for an emergency bearer. Notonly the method disclosed in the second embodiment but also this methodis applicable to the conventional case where the SeNB cannot recognizewhether a bearer for which the execution of DC is requested from theMeNB is for an emergency service.

Another method of solving the problem described in this modificationwill be disclosed.

The SeNB may notify in advance a neighboring eNB of the informationindicating that its own cell does not allow the establishment of anemergency bearer. The neighboring eNB may be an eNB that is possiblysubjected to DC. The SeNB may notify a neighboring eNB of theinformation via the MME. The MeNB uses this information to judge whetherto perform DC of an emergency bearer to the SeNB. In the case where theSeNB does not allow the establishment of an emergency bearer, the MeNBdoes not perform DC to an emergency bearer using the SeNB. Not only themethod disclosed in the second embodiment but also this method isapplicable to the conventional case where the SeNB cannot recognizewhether a bearer for which the execution of DC is requested from theMeNB is for an emergency service.

In the case where the MME has recognized that the SeNB does not allowthe establishment of an emergency bearer, the MME may notify in advancethe MeNB that possibly performs DC with the SeNB of the identifier ofthe SeNB and the information indicating that the SeNB does not allow theconfiguration of an emergency bearer. The MeNB accordingly uses thisinformation to judge whether to perform DC of an emergency bearer to theSeNB. In the case where the SeNB does not allow the establishment of anemergency bearer, the MeNB does not perform DC to an emergency bearerusing the SeNB.

These methods can prevent the SeNB from allocating a resource for anemergency bearer in the case where the SeNB does not allow theestablishment of an emergency bearer. A system reflecting a localregulation and an operator's policy can be constructed.

Second Modification of Second Embodiment

An attempt to cause an emergency bearer to support DC requiresadditional procedures described in the second embodiment and the firstmodification of the second embodiment, thus increasing the complexity ofthe process as a system. The complicated procedure will reduce thestability of the system.

This modification will disclose the method for constructing a stablesystem.

DC is not performed to an emergency bearer. The eNB judges whether thebearer to which the eNB should perform DC is an emergency bearer injudging whether to perform DC. If a relevant bearer is an emergencybearer, the eNB does not perform DC, that is, does not activate the DCexecution process. If a relevant bearer is not an emergency bearer, theeNB performs DC, that is, enables the DC execution process.

DC is not performed to an emergency bearer as described above, thusenabling the construction of a stable system.

For an emergency bearer, whether to support DC may be appropriatelydetermined in accordance with the status of a communication system.

For example, it may be more preferable to construct a stable system thanto support DC for an emergency bearer in a place with a low demand forhigh throughput (a place not congested). Thus, DC can be performed to anemergency bearer in a place with a high demand for high throughput, andDC is not performed to an emergency bearer in a place with a low demandfor high throughput. The eNB may make a judgment based on a thresholdprovided in the demand for throughput. The threshold may be determinedstatically in advance in, for example, specifications, or may benotified to the eNB by the MME.

As a result, the execution of DC to an emergency bearer can be changedin accordance with the status of the communication system, thus enablinga flexible operation according to the status of the communicationsystem.

For an emergency bearer, whether to support DC may be appropriatelydetermined in accordance with the power consumption of the UE.

For example, upon execution of DC based on architecture 3C, the UE needsto communicate with both the MeNB and the SeNB, leading to an increasein the power consumption of the UE. It is preferred to avoid a situationin which an emergency service will be interrupted due to UE's batteryexhaustion. The power consumption of the UE needs to be reduced as muchas possible in accordance with a situation. Thus, DC can be performed toan emergency bearer if the UE is at a high remaining battery level, andDC is not performed to an emergency bearer if the UE is at a lowremaining battery level.

The UE transmits remaining battery level information to the eNB. The eNBmay receive the UE's remaining battery level information and use theremaining battery level information to judge whether to cause the UE toperform DC to the emergency bearer.

The eNB may notify the UE of a remaining battery level informationrequest message to obtain the remaining battery level information fromthe UE. The eNB may notify the UE through an RRC message or aUE-dedicated message. For example, the eNB may include the informationfor requesting the remaining battery level information in a UEinformation request message and notify the UE of the message. In thecase where the UE information request message includes the informationfor requesting the remaining battery level information, the UE that hasreceived the UE information request message notifies the eNB of a UEinformation response message including the remaining battery levelinformation.

As a result, the eNB can receive the remaining battery level informationfrom the UE, and the eNB can judge whether to support DC for theemergency bearer in accordance with the power consumption of the UE. Foran emergency bearer, whether to support DC can be appropriatelydetermined in accordance with the power consumption of the UE.

Turning a small cell on or off is discussed to reduce the powerconsumption of the small cell or reduce interference in the operation ofa large number of small cells. In the procedure for turning on a smallcell for use in an emergency bearer, the small cell may be configurednot to reject the procedure for turning on the small cell. In the casewhere a small cell is used in the emergency bearer, the small cell maybe configured to reject the procedure for turning off the small cell.The methods disclosed in this embodiment and the modifications thereofare applicable as appropriate as the method used in such a case. Forexample, the information indicating that a message for requestingturning on a small cell is for an emergency bearer is included in thismessage.

Third Embodiment

A problem to be solved in a third embodiment and a solution to theproblem will be described below.

In the current specifications, the UE is allowed to request amodification of bearer resources (allocation or release of resources)from the configured bearer (see 5.4.5 of Non-Patent Document 13). The UErequests a bearer modification for the P-GW via the MME. The P-GW canconfigure EPS bearer QoS-related information, and accordingly, the P-GWthat has received a bearer modification request from the UE modifies theEPS bearer QoS-related information, for example, QCI, GBR, MBR, or ARP.

The MME performs a bearer configuration to the eNB, that is, makes anE-RAB setup request based on the EPS bearer QoS-related informationnotified by the P-GW via the S-GW. The MME configures an E-RAB level QoSparameter. When the P-GW modifies a bearer configuration, the MMEaccordingly modifies the bearer configuration to the eNB.

In the case where DC is not performed to a bearer, the bearer isestablished using one eNB. The configuration of the bearer thus can bemodified in response to a bearer resource modification request from theUE in the conventional specifications.

In the case where DC is performed to a bearer, the configuration of thebearer cannot be modified in response to a bearer resource modificationrequest from the UE in the conventional specifications. The E-RABconfiguration cannot be modified in the MeNB or the SeNB.

In the discussion about DC in 3GPP, it is discussed that the MeNBderives a bearer configuration requested for a SeNB, from the bearerconfiguration requested from the MME in the DC execution process. In theDC execution process, the MeNB requests a resource from the SeNB suchthat a total of a resource provided by the MeNB and a resource providedby the SeNB ensures the E-RAB level QoS requested from the MME or is notlower than the E-RAB level QoS.

The MeNB thus needs to set a value different from that of the E-RABlevel QoS information requested from the MME to the SeNB in some cases.The MeNB includes the E-RAB level QoS information requested for the SeNBin a DC execution request message to the SeNB, for example, a SeNBaddition request message and notifies the SeNB of the message. In thismanner, the MeNB configures a bear to the SeNB.

The mechanism in which the UE requests a modification for the bearerconfiguration of the SeNB, which is performed by the MeNB in DC, is notprovided in a bearer resource modification request from the UE to theP-GW in the conventional specifications. A request for modifying thebearer configuration of the SeNB, or a request for modifying theconfiguration for allocation of bearers to the MeNB and the SeNB cannotbe made.

This embodiment will disclose the method for solving such a problem.

At least one of the bearers of the MeNB and the SeNB (hereinbelow alsoreferred to as a “DC bearer”) can be modified in response to theactivation of the UE. The UE-activated DC bearer modification processmay be provided. The message for the UE-activated DC bearer modificationrequest may be provided.

The UE-activated DC bearer modification process will be disclosed. TheUE makes a DC bearer modification request to the MeNB. The UE notifiesthe MeNB of a DC bearer modification request message.

The following eleven, (1) to (11), will be disclosed as examples of theinformation included in the DC bearer modification request message.

(1) Information indicating a DC bearer modification request message.

(2) Identifier for specifying a bearer, for example, EPS beareridentifier, EPS bearer ID, E-RAB identifier, or E-RAB ID.

(3) Information indicating that a predetermined QoS cannot be retained.

(4) E-RAB level QoS information requested, for example, QCI or GBR.

(5) Information indicating a request for improving the QoS of a SeNB,for example, information indicating a request for improving the E-RABlevel QoS.

(6) Information indicating a request for improving the QoS of a MeNB,for example, information indicating a request for improving the E-RABlevel QoS.

(7) Information indicating a request for modifying a packet flow ratiobetween a MeNB and a SeNB, for example, information indicating a requestfor increasing a ratio of the MeNB or information indicating a requestfor improving a ratio of the SeNB.

(8) SeNB identifier or SCG cell identifier.

(9) UE identifier.

(10) UE aggregate maximum bit rate (AMBR).

(11) Combination of (1) to (10) above.

The MeNB that has received a DC bearer modification request message fromthe UE uses the information included in the message to modify the bearerconfiguration of the SeNB or the configuration for allocation of bearersto the MeNB and the SeNB. In this case, the MeNB may make a modificationsuch that a total of the resource provided by the MeNB and the resourceprovided by the SeNB ensures the E-RAB level QoS requested from the MMEor is not lower than the E-RAB level QoS.

The MeNB activates the SeNB modification procedure to perform themodified bearer configuration to the SeNB. The MeNB may include theE-RAB level QoS information requested for the SeNB in a message andnotify the SeNB of the message.

The MeNB may judge not to perform a bearer configuration to the SeNB. Inother words, the MeNB may judge to release the bearer configuration tothe SeNB. This increases modification alternatives. The MeNB mayactivate the SeNB release procedure.

The MeNB may modify a packet flow ratio between a MeNB and a SeNBwithout modifying a DC bearer. This increases modification alternatives.For example, the MeNB may make such a modification in the case ofreceiving the information indicating a request for modifying a packetflow ratio between a MeNB and a SeNB from the UE. This eliminates theneed for performing the process for modifying the bearer configurationof at least any one of the MeNB and the SeNB, resulting in a simplifiedprocedure.

FIG. 22 shows an example of the sequence of the UE-activated DC bearermodification process in a communication system of the third embodiment.

In step ST2301, the SeNB addition procedure is performed among the UE,the MeNB, and the SeNB, so that DC using the MeNB and the SeNB isperformed to the UE (see Non-Patent Document 9). In the case of DCarchitecture 1A, the SeNB addition procedure is performed among the UE,the MeNB, the SeNB, the MME, and the S-GW, so that DC using the MeNB andthe SeNB is performed to the UE.

In this case, the MeNB performs the bearer configuration of the SeNB orthe configuration for allocation of bearers to the MeNB and the SeNB asdescribed above.

In step ST2302, the UE judges whether to request a bearer modification.The UE may judge whether a desired QoS has been obtained for the bearer.Alternatively, the UE may judge whether the QoS for the bearer of theMeNB or the QoS for the bearer of the SeNB has been obtained.

The UE that has judged that a bearer modification does not need to berequested continuously performs DC currently performed.

In step ST2303, the UE that has judged to request a bearer modificationnotifies the MeNB of a DC bearer modification request. The UE may notifythe MeNB of a request through a message provided for the DC bearermodification request. This request may be notified through an RRCmessage or UE-dedicated signaling. The UE may include the informationdescribed above in the DC bearer modification request message.

In step ST2304, the MeNB that has received the message for the DC bearermodification request in step ST2303 uses the information included in themessage to modify the resource configuration of the SeNB. The bearerconfiguration or the configuration for allocation of bearers to the MeNBand the SeNB is modified as the modification of the resourceconfiguration of the SeNB. The E-RAB level QoS information may beconfigured as the bearer configuration. In this case, the MeNB makes amodification such that a total of the resource provided by the MeNB andthe resource provided by the SeNB ensures the E-RAB level QoS requestedfrom the MME or is not lower than the E-RAB level QoS.

In step ST2305, the MeNB activates the SeNB modification procedure forperforming the modified bearer configuration to the SeNB. The MeNB mayinclude the E-RAB level QoS information requested for the SeNB in amessage and then notify the SeNB of the message. As a result, the SeNBmodification procedure is performed among the UE, the MeNB, and theSeNB. In the case of DC architecture 1A, the SeNB modification procedureis performed among the UE, the MeNB, the SeNB, the MME, and the S-GW.The resource configuration of the SeNB is modified through the SeNBmodification procedure.

As a result, the UE can make a DC bearer resource modification request.

In the case where a DC bearer modification is not performed, the MeNBnotifies the UE of a reject message.

A non-limiting example of the case where a DC bearer modification is notperformed is the case where the MeNB makes a judgment. For example, whenreceiving a DC bearer modification request message from the UE, the MeNBjudges that the request from the UE indicated by the informationincluded in the message cannot be satisfied by modifying the resourceconfiguration of the SeNB.

The MeNB may notify the UE of a reject message in response to the DCbearer modification request in such a case.

When receiving a modification reject message from the SeNB in theMeNB-activated SeNB modification procedure, the MeNB may judge that theDC bearer modification request from the UE cannot be satisfied andnotify the UE of a reject message in response to the DC bearermodification request.

Notifying the UE of a reject message in this manner enables the UE torecognize that a DC bearer modification will not be performed. The UEcan use the reject message to judge the execution of another bearermodification means, for example, a conventional UE-activated EPS bearermodification request.

The reject message may include cause information. The following nine,(1) to (9), will be disclosed as examples of the cause information.

(1) A UE-activated DC bearer modification is not supported.

(2) A total of resources of a MeNB and a SeNB is insufficient.

(3) The resource of a MeNB is insufficient.

(4) The resource of a SeNB is insufficient.

(5) The requested EPS level QoS is not accepted.

(6) The EPS bearer identifier is invalid.

(7) The E-RAB identifier is invalid.

(8) A QCI value is not supported.

(9) A SeNB modification request is rejected, in which case the rejectcause information may be included.

The UE that has received the reject message may prohibit the executionof a DC bearer modification request for a predetermined period.

This eliminates the need for unnecessary notification of a DC bearermodification request message, thus reducing a signaling amount.

The predetermined period may be determined statically in advance, forexample, determined in specifications. Determining a predeterminedperiod in advance can facilitate the procedure.

Alternatively, the MeNB may include a predetermined period in a rejectmessage and notify the UE of the message. In this case, the MeNB can seta predetermined period flexibly in accordance with a situation. Thecommunication system can thus be operated flexibly.

It has been disclosed that when receiving a SeNB modification rejectmessage from the SeNB, the MeNB may judge that the DC bearermodification request from the UE cannot be satisfied and notify the UEof a reject message in response to the DC bearer modification request.

In another method, when receiving a SeNB modification reject messagefrom the SeNB, the MeNB may judge that a DC bearer modification requestfrom the UE cannot be satisfied and activate the change of the SeNB tobe used in DC. In the presence of another SeNB capable of DC to the UE,the MeNB may activate the process for changing the current SeNB to theother SeNB. The DC bearer modification request from the UE can thus besatisfied.

First Modification of Third Embodiment

This modification will disclose another method for solving the problemin the third embodiment.

The UE makes a DC bearer modification request to the MeNB via the MME.The UE notifies the MME of a DC bearer modification request message.

The information disclosed in the third embodiment is applicable as theinformation included in the DC bearer modification request. Otherexamples of such information will be described below.

(1) The identifier of a MeNB performing DC, which may be the identifierof a PCell. The identifier of a MeNB performing DC. Or, the informationmay be the identifier of a PCell. This information is applicable incombination with the information disclosed in the third embodiment.

For example, the MME does not need to recognize that DC is beingperformed in DC architecture 3C. In such a case, the MME thus cannotperform a procedure corresponding to a DC bearer modification requestmessage even when receiving the message from the UE.

The MME that has received the DC bearer modification request messagefrom the UE can use the information (1) disclosed above to recognize theMeNB performing the DC.

The MME that has received the DC bearer modification request messagefrom the UE notifies the MeNB performing DC of the DC bearermodification request message. The information disclosed in the thirdembodiment is applicable as the information included in the DC bearermodification request message.

The MeNB that has received the DC bearer modification request messagefrom the MME uses the information included in the message to, forexample, modify the bearer configuration of the SeNB or theconfiguration for allocation of bearers to the MeNB and the SeNB. Themethods disclosed in the third embodiment are applicable to theseprocedures.

FIG. 23 shows another example of the sequence of the UE-activated DCbearer modification process in the communication system of the thirdembodiment. The same steps as those of FIG. 22 will be denoted by thesame step numbers, and description thereof will be omitted.

In step ST2401, the UE that has judged to request a bearer modificationin step ST2302 notifies the MME of a DC bearer modification request. TheUE may provide a message for the DC bearer modification request andnotify the message. The request may be made through a NAS message. TheUE may notify the MME via the MeNB. The UE may notify the MeNB throughan RRC message, and the MeNB may notify the MME through the S1 message.

UE-dedicated signaling may be used. The UE may include the informationdescribed above in the DC bearer modification request message.

The MME that has received the message for DC bearer modification requestin step ST2401 uses the information included in the message torecognize, for example, that the request is a DC bearer modificationrequest, and a MeNB that performs the DC.

In step ST2402, the MME notifies the MeNB that is to perform DC of theDC bearer modification request message. This request may be made throughan S1 message or through UE-dedicated signaling. The MME may include theinformation disclosed in the third embodiment in the DC bearermodification request message.

The MeNB accordingly receives the DC bearer modification request messagefrom the UE.

The process after the MeNB has received the DC bearer modificationrequest message in step ST2402 is similar to that of the thirdembodiment, and accordingly, description thereof will be omitted.

The UE can thus request a DC bearer resource modification as in thethird embodiment.

The message for a DC bearer modification request notified to the MME bythe UE may be a UE-activated request bearer resource modificationmessage notified to the MME by the UE in the conventionalspecifications.

In this case, the message may include the information indicating thatthe message is notified for a DC bearer modification request and theidentifier information about a MeNB performing the DC, fordifferentiation from the conventional information. The message mayinclude the information disclosed in the third embodiment and theinformation disclosed above.

The MME may use the information above to judge whether to make a bearerresource modification request to the P-GW, which is the procedure in theconventional specifications, or make a DC bearer modification request tothe MeNB. For example, the MME may make a DC bearer modification requestto the MeNB in the case of the DC bearer modification request or make abearer resource modification request to the P-GW in other cases.

This eliminates the need for newly providing a message from the UE tothe MME, thus preventing the message procedure from becomingcomplicated.

In notifying the UE of a reject message, the MeNB may notify the UE viathe MME. In this case, the reject message may include the informationdisclosed in the third embodiment, as well as the information indicatingthat the message is provided to reject the DC bearer modificationrequest, and the identifier of the UE that has made the DC bearermodification request. The MME can notify the UE of the reject message.

Although the second embodiment has disclosed the method of making DCapplicable to an emergency bearer, a DC bearer may not be modified inthe case of an emergency bearer.

For example, the UE may avoid requesting a DC bearer modification for anemergency bearer.

In another example, the MeNB may reject a DC bearer change request to anemergency bearer even when receiving the request from the UE. Theinformation indicating that the rejection is for an emergency bearer maybe provided as the cause information and included in a reject message.

Fourth Embodiment

A problem to be solved in a fourth embodiment and a solution to theproblem will be described below.

The current 3GPP specifications include functionalities regarding the UElocation information. A non-limiting example of such functionalities isimmediate minimization of drive test (MDT) functionality in MDT (see3GPP TS37.320 V12.0.0, which will be hereinbelow referred to as“Non-Patent Document 15” as well). The immediate MDT is applicable tothe UE in RRC_Connected. The immediate MDT is performed through the RRCmeasurement procedure. In the measurement configuration, whetherlocation information is included in a measurement report is configuredfor the UE. When such a configuration is performed, the UE includeslocation information in a measurement report and notifies the eNB of thereport.

Upon notification of another configuration message (OtherConfig)including predetermined information (obtain Location) by the eNB, the UEincludes detailed location information based on a global navigationsatellite system (GNSS) in the location information and notifies theinformation when transmitting a measurement report.

The UE measures the detailed location information with a highly accurateGNSS. Due to the use of the GNSS, however, the UE cannot measure theinformation in the indoor environment, for example, in an undergroundmall or an underground garage. In such a case, another piece of highlyaccurate location information is thus required.

This embodiment will disclose the method of solving such a problem.

In the case where location information is configured to be included in ameasurement report in the measurement configuration, the UE performingDC includes a SeNB identifier in the measurement report as the locationinformation and notifies the MeNB of the information. A global eNBidentifier (ID) may be configured as the SeNB identifier. Alternatively,the UE may include the SCG cell identifier as the location informationand notify the MeNB of the information. The UE may configure a CGI orPCI as the cell identifier.

The following five, (1) to (5), will be disclosed as specific examplesof the SCG cell.

(1) All SCG cells configured for DC.

(2) A SPCell.

(3) A SCG cell with the best reception quality (which may be receptionpower).

(4) A SCG cell with the smallest path loss.

(5) A cell of the smallest cell size.

The MeNB can accordingly recognize the location of the UE with anaccuracy corresponding to the coverage size of the SCG cell. It has beendescribed above that the coverage size of the SCG cell is relativelysmall. It is conceivable that a SCG cell having a particularly smallcoverage size will be operated in the indoor environment. Highlyaccurate location information is thus obtained.

Although the MeNB is notified, an eNB having an RRC functionality may benotified in DC.

Another method will be disclosed.

Information indicating a report of the identifier on a SeNB or a SCGcell is newly provided. The eNB may notify the UE of the informationthrough an RRC message. The information may be included in anotherconfiguration message (OtherConfig) and notified. When being notified ofthe information indicating a report on the identifier of the SeNB or theSCG cell through the other configuration message, the UE performing DCmay include the identifier of the SeNB or the SCG cell in themeasurement report and notify the MeNB of the report. Newly providingthe information enables the eNB to explicitly request a report on theidentifier of the SeNB or the SCG cell. This method enables the eNB toobtain the UE location information flexibly as appropriate.

Alternatively, the existing information may be used. When being notifiedof predetermined information (obtain Location) through anotherconfiguration message, the UE performing DC may include the identifierof the SeNB or the SCG cell in a measurement report and notify the MeNBof the report.

In the use of the existing information, the UE may include theidentifier of the SeNB or the SCG cell in a measurement report andnotify the MeNB of the report in the case where the GNSS is unavailableto the UE.

The use of the existing information eliminates the need for providingnew information, thus preventing the process from becoming complicatedas a system.

Another RRC message, not the measurement report, may be used to includethe identifier of the SeNB or the SCG cell therein and notify the MeNB.An RRC message for notification of the information may be newlyprovided. The use of a message different from the measurement reportenables the eNB to obtain the UE location information more flexibly.

The use of the method disclosed in this embodiment enables the eNB toobtain detailed location information about the UE. The eNB can recognizein the coverage of which SeNB or which SCG cell the UE is located.

The method disclosed in this embodiment is applicable to the case wherea radio link failure (RLF) or a handover failure (HOF) has occurred.

When the UE performing DC has an RLF or a HOF, the UE may include theidentifier of the SeNB or the SCG cell in the RLF report message as thelocation information.

When receiving the message including the RLF report request from theeNB, the UE may notify the eNB of an RLF report message including thelocation information.

For example, the message including an RLF report request may be a UEinformation request message. The eNB configures RLF report requestinformation in a UE information request message and notifies the UE ofthe message. The UE that has received the RLF report request informationincludes the location information including the identifier of the SeNBor the SCG cell in a UE information response message and notifies theeNB of the message.

The eNB can accordingly obtain the detailed location information about aUE in which an RLF or a HOF has occurred.

The current 3GPP specifications include other functionalities regardingthe UE location information. Examples of such functionalities include UEpositioning (see 3GPP TS36.305), LTE positioning protocol (LPP, see 3GPPTS36.355), and location service (LCS, see 3GPP TS23.271). In thesefunctionalities, the identifier of the SeNB or the SCG cell may be usedas the UE location information. The identifier of the SeNB or the SCGcell connected to the UE during DC is used as the UE location forderivation.

The UE performing DC using the SeNB is located within the coverage ofthe SeNB. When up to the SCG cell is specified further, the UEperforming DC using the SCG cell is located within the coverage of theSCG cell. Thus, the use of the identifier of the SeNB or the SCG cellconnected to the UE during DC enables the location of the UE to bederived. As described above, the coverage size of the SCG cell isrelatively small. Thus, highly accurate UE location information isobtained.

For example, an enhanced cell ID (E-CID) mechanism is used in thesefunctionalities. This mechanism uses the information about the servingeNB or cell for the UE to obtain the location of the UE. Thus, the UEduring DC has conventionally used the information about the MeNB orPCell.

In a new method, the UE during DC uses the information about the SeNB orthe SCG cell connected to the UE during the DC to obtain the location ofthe UE. The information about the SeNB or the SCG cell may be the eNBidentifier or the cell identifier. The information about thetransmission or reception time between the UE and the SeNB or the SCGcell may be used. For example, a time difference between thetransmission and reception of the UE (UE Tx-Rx time difference) may beused. As a result, the UE location information whose accuracy is higherthan the accuracy of the conventional E-CID method using a MeNB isobtained.

First Modification of Fourth Embodiment

A problem to be solved in a first modification of the fourth embodimentand a solution to the problem will be described below.

The current 3GPP specifications include functionalities regarding themobility state of the UE. Examples of the functionalities include speeddependent scaling of measurement related parameters (see 3GPP TS36.331V12.1.0, which will be hereinbelow referred to as “Non-Patent Document16” as well).

The eNB configures parameters of the mobility state indicating themoving speed of the UE to the UE through the measurement configuration.Examples of the parameters include a measurement period, a threshold ofthe number of HOs, and a scaling factor. The UE that has received themeasurement configuration detects the number of HOs within a measurementperiod. The UE uses the detected number of HOs and the threshold of thenumber of HOs to derive the mobility state of the UE. The mobility stateis classified as “high”, “medium”, or the other (hereinbelow alsoreferred to as “normal”). The UE that has derived the mobility state ofthe UE derives a scaling factor corresponding to the mobility state,multiplies the value of a measurement-related parameter by the scalingfactor, and configures a resultant value. A non-liming example of themeasurement-related parameter is a time to trigger (TTT).

In the conventional specifications, the UE detects the number of HOs toderive the mobility state of the UE as described above.

The UE performing DC changes the MeNB through HO but does not change theSeNB through HO. The mobility state of the UE performing DC isaccordingly judged using the MeNB. For example, in the case where the UEperforming DC moves within the MeNB, the mobility state is set to“normal”.

The small cell, however, has a relatively small coverage. The UE thusmoves between SeNBs or between SCG cells in a short period. In such acase, the mobility state of the UE is no longer substantially “normal”.

The measurement of the SCG cell is used for the MeNB to judge theconfiguration of the SeNB or the SCG cell to be used in DC. It is notsufficient to use the mobility state of the UE, which is judged based onthe number of HOs of the MeNB, in the configuration of ameasurement-related parameter of the SCG cell. The measurement of theSCG cell requires the configuration of a more accuratemeasurement-related parameter, that is, a measurement-related parametersuitable for the coverage of the small cell. Such a configurationrequires the acquisition of a more accurate mobility state of the UE.

This modification will disclose the method of obtaining a more accuratemobility state of the UE.

The number of changes of the SeNB is used to derive the mobility stateof the UE performing DC. The UE performing DC detects the number ofchanges of the SeNB. The UE may record the detected number of changes ofthe SeNB.

The MeNB instructs the UE to count the number of changes of the SeNBwhen performing the procedure for adding a SeNB to be used in DC.Notification may be made through RRC signaling or dedicated signaling.

The information that instructs the detection of the number of changes ofa SeNB may be included in an RRC message and notified. For example, theMeNB may include the information in an RRC connection reconfigurationmessage and notify the UE of the message. The information may beincluded in a “Radio Resource Configuration Dedicated” message andnotified. In another example, the MeNB may include the information in ameasurement configuration and notify the UE of the configuration. Theinformation may be included in a measurement report configuration andnotified. The measurement configuration may be the measurementconfiguration of the SeNB or the SCG cell to be used in DC.

In another example, the MeNB may notify the UE of the information whenperforming an RRC connection reconfiguration regarding the SeNB. Forexample, the MeNB may notify the UE of the information in the SeNBaddition procedure. In another example, the MeNB may notify the UE ofthe information in the SeNB change procedure or the SeNB modificationprocedure. In still another example, the MeNB may notify the UE of theinformation when changing a SPCell.

These notification methods may be used in combination, thus enabling aflexible operation as a system.

The UE that has received an instruction to detect the number of changesof a SeNB detects the number of changes of a SeNB and uses the detectionresult to derive the mobility state of the UE.

A specific example of the method of deriving the mobility state of a UEwill be disclosed. The MeNB instructs the detection of the number ofchanges of a SeNB and also configures a parameter of the mobility stateindicating the moving speed of the UE. This parameter is a parameterrelated to the SeNB. Examples of the parameter include a measurementperiod, a threshold of the number of changes of a SeNB, and a scalingfactor.

The UE that has received the parameter configuration detects the numberof changes of a SeNB within the measurement period. The UE uses thedetected number of changes of a SeNB and the threshold of the number ofchanges of a SeNB to derive the mobility state of the UE. The mobilitystate is classified as “high”, “medium”, or the other (hereinbelowreferred to as “normal”).

As a result, the UE can derive the mobility state of the UE.

The UE that has derived the mobility state of the UE derives a scalingfactor corresponding to the mobility state and multiplies ameasurement-related parameter by the scaling factor. A non-limitingexample of the measurement-related parameter is a TTT.

The measurement-related parameter multiplied by the scaling factorderived using the number of changes of a SeNB, which has been detectedby the UE, is used to measure the SeNB or the SCG cell.

As a result, the UE can detect the number of changes of a SeNB and usethe detection result to derive a more accurate mobility state of the UE.

The use of the mobility state to measure the SCG cell enables the UE toconfigure a more accurate measurement-related parameter, that is, ameasurement-related parameter suitable for the coverage of a small cell.

The use of the method disclosed in this modification enables the UE toconfigure a more accurate measurement-related parameter, that is, ameasurement-related parameter suitable for the coverage of a small cell.The MeNB can obtain a more accurate measurement result of the SCG cellfrom the UE. The MeNB can thus judge the configuration of a SeNB or aSCG cell to be used in DC more accurately in accordance with themobility state of the UE.

As a result, the throughput of the UE can be improved, and also, thecommunication capacity can be improved as a system.

In the method above, the MeNB includes the information that instructsthe detection of the number of changes of a SeNB in an RRC message andnotifies the UE of the message, so that the UE detects the number ofchanges of a SeNB and uses the detection result to measure the SCG cell.

In another method, the MeNB notifies the UE of the configuration of theparameter of the mobility state indicating the moving speed of the UE,which relates to the SeNB, in place of instructing the detection of thenumber of changes of a SeNB. When receiving the configuration of theparameter of the mobility state indicating the moving speed of the UE,which relates to the SeNB, the UE detects the number of changes of aSeNB and uses the detection result to measure the SCG cell.

As a result, the information that instructs the detection of the numberof changes of a SeNB and signaling for the information can be reduced.

Although it has been disclosed that the number of changes of a SeNB isused to derive the mobility state of the UE performing DC, the number ofchanges of a SPCell may be used. The UE performing DC detects the numberof changes of a SPCell. The UE may record the detected number of changesof a SPCell. As a result, a change of a SPcell within a SeNB can betaken into consideration, and a more detailed mobility state of the UEcan be derived.

The number of changes of a SCG cell may be used. The UE performing DCdetects the number of changes of a SCG cell. The UE may record thedetected number of changes of a SCG cell. Also when the SeNB isperforming CA through the RRH or the like, the number of changes of aSCG cell can be recorded to derive a more detailed mobility state of theUE.

Whether to use the number of changes of a SeNB, whether to use thenumber of changes of a SPCell, or whether to use the number of changesof a SCG cell may be selected as appropriate. The MeNB may instruct theUE which number of changes to use. The MeNB may notify the UE of theinformation about which number of changes to use together with theinformation that instructs the detection of the number of changes.

FIG. 24 shows an example of the sequence of a SCG cell measurementprocess in a communication system of the first modification of thefourth embodiment.

In step ST2501, the MeNB notifies the SeNB (S-SeNB herein) of a SeNBaddition request message to perform DC to the UE.

In step ST2502, the SeNB that has received the SeNB addition requestmessage in step ST2501 and judged that the resource of the SeNB isavailable for DC notifies the MeNB of a SeNB addition requestacknowledge message.

In step ST2503, the MeNB that has received the SeNB addition requestacknowledge message notifies the UE of the configuration for causing theUE to perform DC. An RRC connection reconfiguration message is used inthis notification. To cause the UE to detect the number of changes of aSeNB, the MeNB includes the configuration of a parameter of the mobilitystate indicating the moving speed of the UE, which relates to the SeNB,in the message.

The UE that has received the message in step ST2503 performs theresource configuration for the execution of DC.

In step ST2504, the UE notifies the MeNB of an RRC connectionreconfiguration complete message.

In step ST2505, the MeNB notifies the SeNB of a SeNB reconfigurationcomplete message.

In step ST2506, accordingly, a DC execution process is performed amongthe UE, the MeNB, and the SeNB.

The UE that has received the RRC connection reconfiguration message instep ST2503 and recognized that the message includes the configurationof the parameter of the mobility state indicating the moving speed ofthe UE, which relates to the SeNB, assumes that it has been instructedto detect the number of changes of a SeNB, and in step ST2513, uses theparameter to perform the SCG cell measurement process.

Specifically, in step ST2507, the UE detects the number of changes of aSeNB within a measurement period.

In step ST2508, the UE uses the detected number of changes of a SeNB andthe threshold of the number of changes of a SeNB to derive the mobilitystate of the UE. The mobility state is classified as “high”, “medium”,or the other (hereinbelow referred to as “normal”).

In step ST2508, the UE derives a scaling factor (SF) corresponding tothe derived mobility state of the UE.

In step ST2509, the UE multiplies the measurement-related parameter, forexample, TTT by the derived scaling factor. The resultant value is setto the TTT for measuring the SCG cell, and the SCG cell is measured.

In step ST2510, the UE notifies the MeNB of the measurement result. Themeasurement result also includes the measurement result of the SCG cell.

In step ST2511, the MeNB that has received the measurement resultincluding the SCG cell from the UE in step ST2510 uses the measurementresult to determine to change the SeNB. The MeNB that has determined tochange the SeNB activates a SeNB change procedure, so that the SeNBchange procedure is performed among the UE, the MeNB, the S-SeNB, andthe T-SeNB. The S-SeNB is a SeNB before change, that is, a source SeNB.The T-SeNB is a SeNB after change, that is, a target SeNB.

In step ST2513, the UE continuously uses the parameter of the mobilitystate indicating the moving speed of the UE, which relates to the SeNB,to perform the SCG cell measurement process.

The SeNB has been changed in step ST2511, and accordingly, the number ofchanges of a SeNB within the measurement period is incremented by one.The UE uses the detected number of changes of a SeNB and the thresholdof the number of changes of a SeNB to derive a new mobility state of theUE. The UE derives a measurement-related parameter from the newlyderived mobility state of the UE to measure the SCG cell.

In step ST2512, the UE notifies the MeNB of a measurement result. Themeasurement result also includes the measurement result of the SCG cell.

The UE detects the number of changes of a SeNB in this manner to derivea more accurate mobility state of the UE.

The UE uses the mobility state in the measurement of the SCG cell toconfigure a more accurate measurement-related parameter, that is, ameasurement-related parameter suitable for the coverage of the smallcell.

The MeNB can thus obtain a more accurate measurement result of the SCGcell from the UE, and accordingly, can more accurately judge theconfiguration of the SeNB or the SCG cell to be used in DC in accordancewith the mobility state of the UE.

The method disclosed in this modification may be performed separatelyfrom the conventional procedure for deriving the mobility state for eNB.The conventional procedure for eNB, that is, the procedure for derivingthe mobility state from the result on the detection of the number of HOsmay be performed separately from or in parallel with the methoddisclosed in this modification, that is, the procedure for deriving themobility state from the result on the detection of the number of changesof a SeNB.

The method of deriving a mobility state and the measurement methoddisclosed in this modification may be dedicated to the measurement of aSCG cell. This enables an appropriate measurement according to thecoverage range of a cell.

The conventional method of deriving a mobility state and theconventional measurement method can be used to measure the MeNB.

The method of deriving a mobility state and the measurement method,disclosed in this modification, may be used to measure the frequencylayer of a SCG cell or to measure a frequency layer at which a smallcell is operated.

An appropriate measurement according to the coverage range of a smallcell as well as a SCG cell can be performed.

The source MeNB may notify the target MeNB (eNB) of the configuration ofthe parameter of the mobility state indicating the moving speed of theUE, which relates to the SeNB. For example, in the case of a change of aMeNB or a HO of an eNB, the target MeNB (eNB) can accordingly recognizethe parameter configuration of the mobility state indicating the movingspeed of the UE, which relates to the SeNB, configured by the sourceMeNB for the UE being a HO target. The target MeNB can thus contributeto the parameter configuration of the mobility state indicating themoving speed of the UE, which relates to the SeNB, in the MeNB (eNB).

Also in the target MeNB (eNB), the parameter configuration of themobility state indicating the moving speed of the UE, which is the sameas that of the source MeNB, may be continuously made effective until anew parameter configuration of the mobility state indicating the movingspeed of the UE is performed. The UE continuously uses the parameterconfiguration of the mobility state indicating the moving speed of theUE, which is the same as that of the source MeNB, to detect and recordthe number of changes of a SeNB until the target MeNB (eNB) notifies theUE of a new parameter configuration of the mobility state indicating themoving speed of the UE. This enables the long-term detection of themobility state of the UE.

Conversely, the UE may reset the detection and record of the number ofchanges of a SeNB through HO of the MeNB (eNB). The measurement of theSCG cell using the number of changes of a SeNB may be reset inaccordance with the reset of the detection and record of the number ofchanges of a SeNB. The UE may perform the measurement again inaccordance with the reception of the measurement configuration notifiedby a MeNB (eNB) being a change destination. This eliminates the need fornotifying a target MeNB of the measurement configuration by a sourceMeNB. An increase in signaling amount during HO can therefore beprevented.

Although this modification has described HO of a MeNB (eNB), thismodification is also applicable to the case where a serving cell thatnotifies the UE of the measurement configuration is changed, forexample, in the case where a MeNB is changed or a PCell is changed.

The detection and record of the number of changes of a SeNB may be resetwhen a SeNB release procedure is performed. The UE may reset thedetection and record of the number of changes of a SeNB when beingnotified of the SeNB release procedure. The UE may reset the detectionand record of the number of changes of a SeNB upon completion of DC.

The measurement of a SCG cell using the number of changes of a SeNB maybe reset in response to the reset of the detection and record of thenumber of changes of a SeNB.

The method disclosed in this modification may be applied to TTT, as wellas to any other measurement-related parameter. The method can be used inthe case where a more accurate mobility state is required.

Second Modification of Fourth Embodiment

A problem to be solved in a second modification of the fourth embodimentand a solution to the problem will be described below.

The current specifications of 3GPP include the functionalities regardingthe mobility state of a UE. A non-limiting example of thefunctionalities is mobility history information (see Non-Patent Document16).

The mobility history information is applied to UEs in RRC_Idle andRRC_Connected. In response to a change of the serving cell duringRRC_Idle or a change of the PCell during RRC_Connected, the UE recordsthe cell identifier of the cell (cell before change) and a time of stayin the relevant cell. To first enter the E-UTRA cell from anout-of-service area or from another RAT, the UE records only the time ofstay in the area out of the E-UTRA.

The UE includes the recorded cell identifier of the PCell or the servingcell and the time of stay in a UE information response message inresponse to the UE information request from the eNB and notifies the eNBof the message. The eNB can thus obtain the mobility state of the UE.

As described above, the PCell is a target cell during RRC_Connected inthe conventional specifications.

The SCG cell used in DC is not the PCell, and thus is not a target ofthe mobility history information. The mobility state of the UEperforming DC is determined in response to a change of the PCell for theMeNB.

As described in the first modification of the fourth embodiment,accordingly, an eNB cannot obtain the accurate mobility state of the UEthat is suitable for the coverage of a small cell in the conventionalspecifications.

This modification will disclose the method in which the eNB obtains moreaccurate mobility state of the UE.

The UE records the cell identifier of the SPCell performing DC and thetime of stay in the cell. In response to a change of a SPCell, the UEperforming DC records the cell identifier of the cell (cell beforechange) and the time of stay in the relevant cell. The UE may record thecarrier frequency of the cell. The cell identifier may be CGI or PCI.

The UE may separately provide a list in which the information about aconventional PCell is recorded and a list in which the information abouta SPCell is recorded. The UE records the information about a PCell andthe information about a SPCell in the different lists.

The method in which the eNB obtains the list recorded by the UE will bedisclosed.

The MeNB requests the list in which the information about the SPCell isrecorded for the UE performing DC. An RRC message for the request may benewly provided and notified. Alternatively, the information indicatingthat the list in which the information about the SPCell is recorded isrequested may be included in the existing RRC message and notified.Notification may be made through dedicated signaling.

For example, the MeNB may include the information in an RRC connectionreconfiguration message and notify the UE of the message. Theinformation may be included in a “Radio Resource ConfigurationDedicated” message and notified.

The MeNB may notify the UE of the information when performing an RRCconnection reconfiguration regarding the SeNB. In one example, the MeNBmay notify the UE of the information in performing a SeNB additionprocedure. In another example, the MeNB may notify the UE of theinformation when performing the SeNB change procedure or the SeNBmodification procedure. In still another example, the MeNB may notifythe UE of the information when changing a SPCell.

These notification methods may be used in combination, resulting in aflexible operation as a system. In another example, the information maybe included in a UE information request message that is the same messageas the conventional message. The message may include the informationindicating either of the list where the information about a PCell isrecorded or the list where the information about a SPCell is recorded isrequested.

When receiving a request for the list in which the information about aSPCell is recorded from the MeNB, the UE notifies the MeNB of the listin which the information about a SPCell is recorded. The UE may newlyprovide an RRC message for the request for notification. Alternatively,the UE may include the information indicating that the list in which theinformation about a SPCell is recorded is requested in the existing RRCmessage for notification. Notification may be made through dedicatedsignaling.

For example, when using the UE information request message that is thesame as the conventional message to request the list in which theinformation about a SPCell is recorded, the UE may use the UEinformation response message for notification. The UE includes the listin which the information about a SPCell is recorded in a UE informationresponse message and notifies the MeNB of the message.

The MeNB may individually request the list in which the informationabout a PCell is recorded and the list in which the information about aSPCell is recorded for the UE. For example, the UE information requestmessage may be used for both the requests. The UE can recognize whichinformation the UE will notify the MeNB by including the informationindicating either of the list, where the information about a PCell isrecorded, or the list, where the information about a SPCell is recorded,in the message. The UE may report a corresponding list to the MeNB inaccordance with the information.

The MeNB may request both the list in which the information about aSPCell is recorded and the list in which the information about a PCellis recorded through one message. The MeNB may notify the UE of theinformation indicating that the MeNB will request both the lists. The UEthat has received the message notifies the MeNB of both the list inwhich the information about a SPCell is recorded and the list in whichthe information about a PCell is recorded. Notification may be madethrough one message.

One message may always indicate that both the lists are requested, whichmay be determined statically in advance in, for example, specifications.When the MeNB notifies the UE of the message, the UE notifies the MeNBof both the list in which the information about a SPCell is recorded andthe list in which the information about a PCell is recorded.Notification may be made through one message.

The method of creating the list in which the information about a SPCellis recorded will be disclosed.

In response to a change of a SPCell during DC, the UE records, forexample, the cell ID of the cell (cell before change) and the time ofstay in the cell. The UE may also record the carrier frequency of thecell or the cell size of the cell.

The maximum number of cells to be recorded in a list may be determined.For example, n cells may be recorded at the maximum, and if the numberof cells exceeds n, the UE discards the extra cells, starting with theoldest cell record. The recording capacity of the UE can be preventedfrom increasing enormously. The maximum number of cells n may bedetermined statically in, for example, specifications or may be notifiedby the MeNB.

The UE may discard the list in which the information about a SPcell isrecorded when the SeNB release procedure is performed. The UE may newlycreate the list in which the information about a SPcell is recorded whenthe SeNB addition procedure is performed. The case where the SeNBrelease procedure is performed may be the case where the UE releases orresets the resource for the SeNB.

When the SeNB release procedure is performed, the UE may retain the listin which the information about a SPCell is recorded for a predeterminedperiod. When a SeNB addition procedure is newly performed before theexpiration of a predetermined period from the execution of the SeNBrelease procedure, the UE records the information about a SPCell in thelist that has been created. When a predetermined period expires from theexecution of the SeNB release procedure without the SeNB additionprocedure being newly performed, the UE discards the list.

As a result, even when DC is intermittently performed in a situation inwhich the coverage of the SeNB is not seamless, the list in which theinformation about a SPCell is recorded will not be discardedunnecessarily. A predetermined period may be determined statically inadvance in, for example, specifications. Alternatively, a predeterminedperiod may be notified to the UE by the MeNB. In a notification method,a predetermined period may be notified through RRC message or throughdedicated signaling. Alternatively, the MeNB may broadcast thepredetermined period to the UE being served thereby. The predeterminedperiod may be included in the SIB and notified.

The UE may record the time in which DC is not performed duringRRC_CONNECTED. For example, the UE may record a time from a shift toRRC_CONNECTED to the execution of the SeNB addition procedure, a timefrom the execution of the SeNB release procedure to the execution of theSeNB addition procedure, or a time from the execution of the SeNBrelease procedure to the end of the RRC_CONNECTED state. The UE mayrecord the respective times separately. The UE may record the respectivetimes at the occurrence of a time in which DC is not performed. The UEmay avoid recording the cell identifier of the SPCell and the carrierfrequency information during the time in which DC is not performed butmay record the relevant time as a time of stay.

The UE can accordingly record the situation of the change of a SPCell inthe RRC_CONNECTED state also in the case where the SPCell is not used.The MeNB can obtain the information from the UE to recognize moredetailed mobility state of the UE.

The UE may discard the list in which the information about a SPCell isrecorded when a HO of the MeNB is performed.

The UE may retain the list in which the information about a SPCell isrecorded for a predetermined period when a HO of the MeNB is performed.When a SeNB addition procedure or a SPCell change procedure has beenperformed before the expiration of a predetermined period from theexecution of the HO procedure, the UE records the information about aSPCell in the list that has been created. When a predetermined periodexpires from the execution of the HO procedure without the SeNB additionprocedure or the SPCell change procedure being newly performed, the UEdiscards the list.

When a HO of the MeNB is performed, the UE may notify the MeNB (eNB)being a HO destination of the list in which the information about aSPCell is recorded and then discard the list.

The UE may notify the MeNB (eNB) being a HO destination of the list inwhich the information about a SPCell is recorded in response to arequest from the MeNB, after the execution of the HO procedure.

In the case of HO of the MeNB, the MeNB being a HO source may notify theMeNB (eNB) being a HO destination of the list in which the informationabout a SPCell is recorded, which has been obtained from the UE. If thelist does not include the cell size, the MeNB may add the cell size tothe list and notify the list. This is effective in the case where theMeNB has recognized the cell size of the SPCell. Notification may bemade through X2 signaling or through S1 signaling via the MME.

This method allows the MeNB (eNB) being a HO destination to continuouslyuse the information.

The MeNB being a HO source may notify the MeNB (eNB) being a HOdestination of the list in which the information about a SPCell isrecorded, which has been obtained from the UE. Notification may be madetogether with the list in which the information about a PCell isrecorded, which has been obtained from the UE. The lists may be includedin the same message and notified.

In the method described above, the UE records the information about aPCell and the information about a SPCell in the different lists. Inanother method, the UE may record the information about a PCell and theinformation about a SPCell in one list. Alternatively, the informationabout a SPCell may be included in the conventional list of theinformation about a PCell.

In this case, a parameter indicative of a SPCell may be provided and berecorded in association with the SPCell to create a list.

In the case where the list includes a cell size, no parameter indicativeof the SPCell may be recorded.

As a result, the UE can use only one list, thus reducing recordingcapacity and facilitating the list creation procedure. This reducesrequests for a list between the MeNB and the UE and information ormessages included in a notification message. The signaling load cantherefore be reduced.

In the method described above, the UE records the information about aSPCell to create a list. In another method, the UE may record theinformation about a SeNB and create a list. In response to a change of aSeNB, the UE performing DC records the eNB identifier of the SeNB (SeNBbefore change) and a time of stay in the eNB. The UE may record thecarrier frequency used by the eNB. Although the relevant information isnot as refined as the information about a SPCell, the recording capacityand signaling load can be reduced.

The UE may record the information about a SCG cell and create a list. Inresponse to a change of a SCG cell, the UE performing DC records thecell identifier of the SCG cell (SCG cell before change) and a time ofstay in the cell. The UE may record the carrier frequency of the cell ormay also record the cell size of the cell. The MeNB can obtain the listin which the information about a SCG cell is recorded to derive a moredetailed mobility state of the UE.

A list can be selected from among the list in which the informationabout a SPCell is recorded, the list in which the information about aSeNB is recorded, and the list in which the information about a SCG cellis recorded. A list may be determined statically in advance in, forexample, specifications. Alternatively, the MeNB may instruct the UE tocreate which list. The MeNB may notify the UE of the information aboutwhich list to be created. For example, the MeNB may notify the UE inentering the RRC_Connected state. The MeNB may notify the UE through anRRC message or dedicated signaling.

Third Modification of Fourth Embodiment

A problem to be solved in a third modification of the fourth embodimentand a solution to the problem will be described below.

The current 3GPP specifications include functionalities regarding themobility state of a UE. A non-limiting example of such functionalitiesis UE history information (see Non-Patent Document 1).

For the UE history information, the eNB that serves a UE creates a “lastvisited cell list” of an active UE.

When the UE performs HO, the eNB being a HO source adds a PCell to the“last visited cell list” of the UE and notifies the eNB being a HOdestination of the list through S1 or X2. The eNB being a HO destinationperforms a similar procedure to the eNB being a subsequent destinationand notifies the eNB of the list. The network creates and retains theUE's HO history information. Examples of the information recorded in the“last visited cell list” include a cell identifier such as a CGI, a cellsize, a time of stay in a cell, and a HO cause.

In this manner, the eNB records the HO history information in a list inthe conventional specifications.

The SeNB to be used in DC is not changed through HO. No matter how manytimes the UE performing DC repeatedly changes a SeNB, therefore, thechange is not recorded in the list.

In the conventional specifications, thus, the eNB cannot obtain accuratemobility state of the UE that is suitable for the coverage of a smallcell, as described in the second modification of the fourth embodiment.

This modification will disclose another method in which an eNB obtainsmore accurate mobility state of the UE.

The MeNB creates a list of SPCells connected with a UE performing DC. Inthe description below, the list of SPCells that have been connected witha UE performing DC may be referred to as a “SPCell change history list”.

When the SPCell used in DC is changed for the UE, the MeNB adds theSPCell before change to the SPCell change history list. Alternatively,when the SeNB release procedure is performed, the MeNB adds the SPCellthat has been connected with the UE before release to the SPCell changehistory list of the UE.

Examples of the information recorded in the SPCell change history listinclude a cell identifier such as a CGI, a cell size, a time of stay ina cell, a SPCell change cause, and a SeNB release cause.

As a result, the MeNB can record the SPCell history information on theUE performing DC in a list. The MeNB can accordingly obtain the mobilitystate of the UE suitable for the coverage of a small cell.

The MeNB may separately provide the conventional list in which the HOhistory information is recorded and the list in which the SPCell changehistory information is recorded. The MeNB records the HO historyinformation and the SPCell change history information in the differentlists.

When the SeNB release procedure is performed to the UE performing DC,the MeNB may discard the list in which the SPcell change historyinformation on the UE is recorded. When the SeNB addition procedure isperformed to the UE, the MeNB may newly create a list in which theSPcell information on the UE is recorded. The case where the SeNBrelease procedure is performed may be the case where the MeNB instructsthe UE to release the resource of the SeNB.

When the SeNB release procedure is performed to the UE performing DC,the MeNB may retain the list in which the SPCell information on the UEis recorded for a predetermined period. When the SeNB addition procedureis newly performed before the expiration of a predetermined period fromthe execution of the SeNB release procedure to the UE performing DC, theMeNB records the procedure in the list that has been created. When thepredetermined period expires from the execution of the SeNB releaseprocedure to the UE performing DC without the SeNB addition procedurebeing newly performed, the MeNB discards the list.

As a result, even when DC is intermittently performed in a situation inwhich the coverage of the SeNB is not seamless, the list in which theSPCell change history information is recorded will not be discardedunnecessarily. A predetermined period may be determined statically inadvance in, for example, specifications or may be determinedsemi-statically or dynamically. The MME or the operation and maintenance(O&M) may determine a predetermined period and notify the MeNB of thepredetermined period.

The MeNB may record the time in which the MeNB does not perform DC tothe UE in RRC_Connected in a list. For example, the MeNB may record atime from the completion of the RRC connection establishment procedurebetween the UE and the MeNB to the execution of the SeNB additionprocedure, a time from the execution of the SeNB release procedure tothe execution of the SeNB addition procedure, and a time from theexecution of the SeNB release procedure to the end of the RRC_CONNECTEDstate. The MeNB may separately record the times. The MeNB may recordthese times at the occurrence of a time in which DC is not performed.For the time in which DC is not performed, the cell identifier and thecarrier frequency information of the SPCell are not recorded and only atime of stay may be recorded.

The MeNB can accordingly record the situation of the change of a SPCellin the RRC_CONNECTED state also in the case where the SPCell is notused. The MeNB can recognize more detailed mobility state of the UE.

The MeNB may discard the list in which the SPCell change historyinformation on the UE being a HO target is recorded when a HO of theMeNB is performed.

The MeNB may retain the list in which the SPCell change historyinformation on the UE being a HO target is recorded for a predeterminedperiod when a HO of the MeNB is performed. The list is available whenthe UE being a HO target is switched back to the MeNB being a HO source.

In the case of HO of the MeNB, the MeNB being a HO source may notify theMeNB (eNB) being a HO destination of the list in which the SPCell changehistory information is recorded. The list may be notified through X2signaling or through S1 signaling via the MME. This method enables theMeNB (eNB) being a HO destination to continuously use the information.

The MeNB being a HO source may notify the MeNB (eNB) being a HOdestination of the list in which the PCell HO history information isrecorded. The list may be notified together with a list in which theSPCell change history information is recorded. The lists may be includedin the same message and notified.

When receiving a list in which the SPCell change history information onthe UE being a HO target from the MeNB being a HO source, the MeNB (eNB)being a HO destination may retain the list in which the SPCell changehistory information on the UE being a HO target is recorded for apredetermined period.

When the MeNB (eNB) being a HO destination is newly subjected to theSeNB addition procedure or the SPCell change procedure before theexpiration of a predetermined period from the execution of the HOprocedure, the information about a SPCell is recorded in the list thathas been created. The MeNB (eNB) being a HO destination discards thelist when a predetermined period expires without the SeNB additionprocedure or the SPCell change procedure being newly performed.

In the method described above, the MeNB records the PCell HO historyinformation and the SPCell change history information in the differentlists. In another method, the PCell HO history information and theSPCell change history information may be recorded in one list.Alternatively, the SPcell change history information may be included inthe list of the conventional PCell HO history information.

In this case, a parameter indicative of a SPCell may be provided andrecorded in association with the SPCell to create a list.

In the case where the list includes a cell size, no parameter indicativeof the SPCell may be recorded.

As a result, the MeNB can use only one list, thus reducing recordingcapacity and facilitating the list creation procedure.

In the method described above, the MeNB records the SPCell changehistory information to create a list. In another method, the MeNB mayrecord the SeNB change history information and create a list. For the UEperforming DC, the MeNB records the eNB identifier of the SeNB (SeNBbefore change) and a time of stay in the eNB in response to a change ofa SeNB. The MeNB may record the carrier frequency used by the eNB or thechange cause. Although the relevant information is not as refined as theSPCell information, the recording capacity can be reduced.

The MeNB may record the SCG cell change history information to create alist. For the UE performing DC, the MeNB records the cell identifier ofthe SCG cell (SCG cell before change) and a time of stay in the cell inresponse to a change of a SCG cell. The MeNB may record the carrierfrequency of the cell or may also record the cell size of the cell. TheMeNB may record the change cause. The MeNB can obtain the list in whichthe SCG cell change history information is recorded to derive a moredetailed mobility state of the UE.

A list can be selected from among the list in which the SPCell changehistory information is recorded, the list in which the SeNB changehistory information is recorded, and the list in which the SCG cellchange history information is recorded. A list may be determinedstatically in advance in, for example, specifications, or may bedetermined semi-statically or dynamically. The MME or O&M may determinea list and notify the MeNB of the list.

Fifth Embodiment

This embodiment will disclose the method of enabling communications withappropriate amounts of resources such as frequency, time, andtransmission power using a sounding reference signal (SRS) transmittedfrom a UE being a CoMP target at the start of the coordinated multipointtransmission and reception (CoMP) described in Non-Patent Document 7.

Herein, the “sounding reference signal” refers to a training sequencesignal that is always or intermittently transmitted also in the absenceof transmission data as described in, for example, Non-Patent Document14.

First, uplink will be described. FIG. 25 shows the concept of UL CoMPunder discussion of 3GPP. With reference to FIG. 25, an eNB#1 is denotedby reference “5101”, an eNB#2 is denoted by reference “5103”, thecommunication area, that is, coverage of the eNB#1 is denoted byreference “5102”, and the communication area, that is, coverage of theeNB#2 is denoted by reference “5104”. A central entity or a mobilemanagement entity (MME) is denoted by reference “5106”.

When performing UL CoMP, that is, uplink coordinated multiple pointreception, the eNB#1 5101 and the eNB#2 5103 perform a coordinatedoperation between the eNBs via the central entity or the mobilemanagement entity (MME) 5106. For example, coordinated scheduling (CS)in which coordinated multiple point scheduling is performed is studied,where communication data 5107 and communication data 5110 with a UE 5105located at the cell edge, transmission power, and the like can bescheduled in accordance with the communication status of each eNB toimprove a throughput and increase a system throughput. The centralentity is a functional unit for coordinated multiple point. The centralentity exchanges signals for coordinated multiple point between the eNBsin the case of the operation via the MME and the actual coordinationcontrol is performed between the eNBs.

In UL CoMP during CS, the user equipment (UE) 5105 being served by theeNB#1 5101 transmits a scheduling request (SR) to the eNB#1 5101 at theoccurrence of the data 5107 that the UE 5105 wants to transmit to theeNB#1 5101. The eNB#1 5101 confirms the availability of a resource, suchas the communication status of another UE, and transmits a grant signalindicating an allowed range if the transmission is allowed.

When receiving the grant signal, the UE 5105 transmits the data 5107,which the UE 105 wants to transmit, within a range allowed by the grantsignal.

When detecting that the UE 5105 is located at a cell boundary or nearanother cell, the eNB#1 5101 uses radio resource control (RRC) to notifythe UE 5105 of an SRS transmission instruction.

The eNB#1 5101 may determine that the UE 5105 is located at the cellboundary based on whether a report value of its own cell that has beenreported from the UE 5105 through a measurement report message,specifically, reference signal received power (RSRP), reference signalreceived quality (RSRQ), or both of them are not greater than a specificthreshold.

The eNB#1 5101 may determine that the UE 5105 is near another cell basedon whether a report value of another cell that has been reported fromthe UE 5105 through a measurement report message, specifically, RSRP,RSRQ, or both of them are not smaller than a specific threshold.

According to Non-Patent Document 14 (see 5.5.1.5), a parameter n^(RS)_(ID) for generating a pseudo-random number that defines an SRS signalis N^(cell) _(ID), and is a value provided per cell (cell ID). In thepresent invention, at least one UE-dedicated parameter is specified bythe SRS transmission instruction. In other words, the UE 5105 transmitsnot a cell-specific SRS signal but a UE-specific SRS signal.

The SRS signal may always be a UE-specific signal. Alternatively, upondetection that a UE is located at a cell boundary or near another cell,a cell-specific SRS signal may be switched to a UE-specific signal.

The methods of transmitting data by a UE are classified into two methodsbelow. In one of the methods, the same configuration (same PUSCH config,same PUCCH config) is provided when the UE transmits data to the eNB#1and when the UE transmits data to the eNB#2. In the other method, adifferent configuration is provided when the UE transmits data to theeNB#1 and when the UE transmits data to the eNB#2.

For example, in the example shown in FIG. 25, when the UE 5105 transmitsdata to the eNBs 5101 and 5103 using different configurations, the eNB#25103 notifies the eNB#1 5101 of a parameter for CoMP configuration to beused in the eNB#2 5103, such as “PUCCH config” or “PUSCH config”, via anX2 interface 5115. The notification may be made via the central entityor the MME 5106. The eNB#1 5101 notifies the UE 5105 of such configinformation.

In the transmission to the eNB#2 5103, the UE 5101 can thus transmit thedata using the configuration with which the eNB#2 5103 can receive thedata. This method is effective when eNBs are not synchronized with eachother, such as when a large delay time occurs in the backhaul of theeNB.

When the UE 5105 transmits data using a common configurationirrespective of whether transmission is to the eNB 5101 or 5103, theeNB#1 5101 notifies the eNB#2 5103 of a parameter for CoMPconfiguration, such as “PUCCH config” or “PUSCH config”, via the X2interface 5115. The notification may be made via the central entity orthe MME 5106.

The eNB#2 5103 can thus receive the data transmitted from the UE 5105.This method enables the UE to transmit the same data without consideringto which eNB the UE transmits data, thus facilitating the controlprocedure.

The eNB#1 5101 directly notifies the eNB#2 5103 adjacent to the eNB#15101 that possibly performs UL CoMP of an SRS config 5116 via the X2interface 5115. The eNB#2 5103 starts receiving an SRS of the UE 5105 inaccordance with the SRS config 5116.

In this case, it suffices that the eNB#1 5101 and the eNB#2 5103 aresynchronized with each other in advance, or that the eNB#1 5101 and theeNB#2 5103 are synchronized with each other within a specific timerange. It is also effective to achieve synchronization not only betweenOFDM symbols but also between subframe numbers, slot numbers, or systemframe numbers each indicating a time corresponding to an OFDM symbollength (corresponding to those specified in TS36.211).

The eNB is enabled to receive signals within a predetermined time range,which is longer than a CP length, from the designated SRS transmissiontime. It is also effective to make the CP length of only the OFDM symbolof an SRS longer than the CP length of any other piece of data. It isalso effective to provide a slot format of large CP length including thedata portion upon start of the SRS transmission. Alternatively, it isalso effective to change a reference timing of the UE's transmission pereNB, for example, a head timing of the subframe number, slot number, orsystem frame number.

As a result, the eNB#2 5103 that is a UL CoMP target can recognize theuplink communication quality through the reception of an SRS of the UE5105 before starting UL CoMP. Both the eNB#1 5101 and the eNB#2 5103report uplink reception qualities 5109 and 5112 to the central entity5106, thus enabling the central entity 5106 to optimally allocateresources to the two eNBs.

A delay time before the start of UL CoMP (a time during which uplinkquality is measured after an instruction for start) is not required andan immediate start of UL CoMP is enabled, thus eliminating the need forallocation of a yet-to-be-optimized frequency, time, or transmissionpower that occurs during the delay time.

Although transmission is performed via the X2 interface 5115 in themethod of notifying SRS config, transmission may be performed via thecentral entity or the MME 5106.

In this case, the central entity notifies the selected eNB of the eNBidentifier of the eNB#1 5101. The central entity may select a pluralityof eNBs.

The central entity may notify the UE 5105 of the eNB identifier of theselected eNB.

In the procedure before starting CoMP described above, an instruction totransmit an SRS is provided to the UE that is a CoMP target, and then,the SRS config 5116 is notified to the adjacent eNB#2 5103.Alternatively, the adjacent eNB may be notified of SRS config before theUE is notified of SRS config, considering the case where the resourcefor SRS, which is desirably allocated by the adjacent eNB#2 5103, suchas frequency, time (subframe number), or resource block number has beenused.

To prevent the resource for SRS of SRS config and the resource for SRSbeing used by the eNB#2 5103 from being identical to each other, theeNB#2 5103 may notify the eNB (eNB#1 5101) adjacent thereto of the usestatus of a resource upon start of the use of the SRS of the eNB#2.Preventing the use of the same resource as the resource for SRS fromanother UE being served by the eNB#2 5103 further improves the receptionquality of an SRS from the UE in the eNB#2 5103.

In the example in which a start of SRS transmission is judged asdescribed above, the eNB#1 5101 notifies the UE 5105 of an instructionto start SRS transmission at a timing of detection that the UE islocated at the cell boundary, thus minimizing the SRS transmissions whennot used. Alternatively, to omit a processing time for an instruction tostart SRS transmission in the case where, for example, the eNB#1 5101has a small cell radius, SRS transmission start config may be configuredin advance when the UE 5105 starts communicating with the eNB#1 5101.

In the SRS transmission instruction, not a cell-dedicated parameter butat least one UE-dedicated parameter is transmitted in addition to theinformation by which a resource location is designated. Alternatively,for example, an ID for specifying a UE, such as a system architectureevolution (SAE) temporary mobile station identifier (S-TMSI) or aninternational mobile station identifier (IMSI) may be notified (forexample, n^(RS) _(ID)=S-TMSI, n^(RS) _(ID)=IMSI).

Although not a cell-dedicated parameter but at least one UE-dedicatedparameter is transmitted in the SRS transmission instruction, a pool ofSRSs to be used in common within a specific area such as a trackingarea, CoMP set, or a cluster of groups of adjacent cells managed throughclustering may be prepared. In one effective approach, even when groupsof adjacent cells are installed in places inaccessible to radio waves,such as eNBs installed in an underground mall and eNBs installedoutdoors, cells close to each other graphically share an ID for SRS asone group. The central entity or the MME 5106 may mange IDs and notifythe UE of a delivered ID through an SRS instruction via the serving cell(for example, n^(RS) _(ID)=within-area ID).

As a result, an SRS is shared in a specific area, thus enabling the eNBwithin the area to receive the SRS in advance.

In the SRS transmission instruction, not a cell-dedicated parameter buta plurality of cell-dedicated parameters may be notified simultaneouslythrough at least one of time multiplexing, frequency multiplexing, andcode multiplexing, or through a combination thereof. In this case, theeNB#2 5103 transmits SRS config including at least one cell-dedicatedparameter such as a cell ID to the eNB#1 5101. The eNB#1 5101 notifiesthe UE 5105 of this information. The UE 5105 can thus transmit an SRSdedicated to the eNB#2 5103 simultaneously with an SRS dedicated to theeNB#1 5101.

The information that enables the identification of multiplexing of theresources used in the eNB#2 5103 may be notified together with the SRSconfig 5116 notified to the eNB#2 5103 by the eNB#1 5101. This enablesthe eNB#2 5103 to receive the SRS of the UE 5105.

If a transmission bit count decreases due to a change of the SRStransmission approach and the SRS transmission power becomesinsufficient, a corresponding transmission power offset may be added.

Although the eNB#2 5103 that is a notification destination for the eNB#15101 is an adjacent eNB that possibly performs UL CoMP in thedescription above, specifically, the eNB#2 5103 may be an eNB that is anUL CoMP target or all the cells in an UL CoMP set.

Although the SRS transmission instruction to the UE is described usingthe example in which RRC is used, the instruction may be providedthrough MAC signaling or an L1/L2 control, for example, PDCCH/EPDCCH.

Downlink will be described next.

DL CoMP is discussed as in uplink. For example, joint processing (JP) inwhich both cells perform transmissions and CS in which coordinatedmultipoint scheduling is performed are studied. JP is classified asjoint transmission (JT) or dynamic point selection (DPS). A methodinvolving JT and CS in combination is also studied. These methods can beused to improve a throughput at a cell edge and increase a systemthroughput.

Particularly in the case of time division duplex (TDD) of a signal forCoMP, a frequency is the same between uplink and downlink, andaccordingly, a channel can be estimated from an uplink SRS to estimate adownlink channel. The signal can thus be used in DL CoMP.

Description will be given using an example of downlink CS during TDD. InDL CoMP, at the occurrence of data that the eNB #1 5101 wants totransmit to the UE 5105, the eNB#1 5101 transmits data to the UE 5105.

When detecting that the UE 5105 is located at a cell boundary, the eNB#15101 uses RRC to notify the UE 5105 of an SRS transmission instruction.According to Non-Patent Document 14 (see 5.5.1.5), the parameter n^(RS)_(ID) for generating a pseudo-random number that defines an SRS signalis N^(cell) _(ID), which is a value for each cell (cell ID). In thepresent invention, an SRS transmission instruction designates at leastone UE-specific parameter. In other words, the UE 5105 transmits not anSRS signal specific to a cell but an SRS signal specific to a UE.

The eNB#1 5101 directly notifies the eNB#2 5103 adjacent to the eNB#1that possibly performs DL CoMP of SRS config via X2. The eNB#2 startsreceiving an SRS of the UE 5105 in accordance with the SRS config.

As described above, in the case of TDD, the eNB#2 that is a DL CoMPtarget receives an SRS of the UE before starting DL CoMP, therebyrecognizing downlink communication quality. Both the eNB#1 and the eNB#2report the uplink reception quality to the central entity 5106, thusenabling the central entity 5106 to optimally allocate resources to thetwo eNBs.

A delay time until the start of DL CoMP, that is, a time during whichthe UE measures downlink quality after an instruction for start, is notrequired and an immediate start of DL CoMP is enabled, thus eliminatingthe need for allocation of a yet-to-be-optimized frequency, time, ortransmission power that occurs during the delay time.

Modifications are provided for downlink as well as for uplink.

Notification may be made via S1 (via the MME) in the SRS confignotification method. Alternatively, notification may be made via thefunctional unit of the central entity that allocates resource ofinter-eNB CoMP.

In this case, the central entity notifies the selected eNB of the eNBidentifier of the eNB#1 5101. The central entity may select a pluralityof eNBs.

The central entity may notify the UE 5105 of the eNB identifier of theselected eNB.

In the procedure before starting CoMP, the adjacent eNB may be notifiedof SRS config before notification to the UE.

Alternatively, the eNB#2 5103 may notify the adjacent eNB (eNB#1) of theuse status when starting the use of an SRS of the eNB#2.

In the example in which the start of SRS transmission is judged, SRStransmission start config may be configured in advance when the UE 5105starts communication with the eNB#1.

At least one UE-dedicated parameter included in an SRS transmissioninstruction may be the notification of an ID that specifies a UE, suchas S-TMSI or IMS (for example, n^(RS) _(ID)=S-TMSI, n^(RS) _(ID)=IMSI).

In the SRS transmission instruction, a pool of SRSs to be used in commonmay be prepared within a specific area, for example, a tracking area, aCoMP set, or a cluster of groups of adjacent cells managed throughclustering. The central entity or the MME 5106 may mange IDs and notifythe UE of a delivered ID through an SRS instruction via the serving cell(for example, n^(RS) _(ID)=pool ID for SRS).

As a result, an SRS is shared in a specific area, thus enabling the eNBwithin the area to receive an SRS in advance.

Although not a cell-dedicated parameter but at least one UE-dedicatedparameter is transmitted in the SRS transmission instruction, aplurality of cell-dedicated parameters may be notified simultaneouslythrough time multiplexing, frequency multiplexing, code multiplexing, ora combination thereof. In this case, the information that enables theidentification of multiplexing of the resources used in the eNB#2 5103may also be notified through the SRS config 5116 from the eNB#1 5101 tothe eNB#2 5103.

Although the eNB#2 5103 that is a notification destination for the eNB#15101 is an adjacent eNB that possibly performs DL CoMP in thedescription above, specifically, the eNB#2 5103 may be an eNB that is aDL CoMP target or all the cells in a DL CoMP set. Alternatively, theeNB#2 5103 may be a relevant eNB within a tracking area corresponding tothe management of IDs or an eNB in a cluster of groups of adjacent cellsmanaged through clustering. A plurality of relevant eNBs in the trackingarea and a plurality of eNBs in the cluster may be provided.

Although the SRS transmission instruction to the UE is described usingthe example in which RRC is used, the instruction may be providedthrough MAC signaling or an L1/L2 control signal, for example,PDCCH/EPDCCH.

When detecting that the UE 5105 is remote from the cell boundary or thevicinity of another cell, the eNB#1 5101 notifies the eNB#2 5103 of astop of the reception of an SRS via the X2 interface 5115, the MME, orthe central entity 5106.

The eNB#1 5101 may determine that the UE 5105 is not located at the cellboundary based on whether a report value of its own cell (eNB#1) thathas been reported by the UE through a measurement report message,specifically, RSRP, RSRQ, or both of them are not smaller than aspecific threshold.

The eNB#1 5101 may determine that the UE 5105 is remote from thevicinity of another cell based on whether a report value of another cell(eNB#2) that has been reported by the UE through a measurement reportmessage, specifically, RSRP, RSRQ, or both of them are not greater thana specific threshold.

The eNB#1 5101 may notify the eNB#2 of a stop of the reception of an SRSwhen CoMP ends.

The eNB#1 5101 may notify the eNB#2 of a stop of the reception of an SRSwhen a parameter for SRS is designated as a cell-dedicated parameter.

Uplink control and downlink control may be performed simultaneously.

First Modification of Fifth Embodiment

Although the fifth embodiment has described the example of CoMP, thereception of an SRS in DC by an adjacent eNB eliminates a delay timeafter DC is started and a DC configuration is changed, that is,eliminates a time during which the UE measures the downlink qualityafter a start instruction. This enables an immediate start of DC, thuseliminating the allocation of a yet-to-be-optimized frequency, time, ortransmission power that occurs in a delay time.

As described in Non-Patent Document 9 (see Chapter 8), several forms ofDC have been studied, and the studies of architecture 1A andarchitecture 3C are pursued. The example of architecture 3C will bedescribed below with reference to FIG. 27, which will be describedbelow.

A S-GW 5217 allocates two bearers per user. A bearer 1 is a bearer fortransmission from a MeNB 5218 to a UE 5220 via S1-U. In a bearer 2, asignal that has arrived at the MeNB 5218 via S1-U is separated into twoportions by a PDCP processing unit. One portion of the signal issubjected to radio link control (RLC) and MAC processing by the MeNB5218 and transmitted to the UE 5220. The other portion of the signal isprocessed by a SeNB 5219 and transmitted to the UE 5220.

For example, a control signal for managing mobility is applied to thebearer 1, and user packet data such a video is applied to the bearer 2.This enables the UE to continuously perform communication even whilemoving at high speed in the MeNB having a large cell radius. The SeNBhas a small cell radius, in which a few users can use the frequencybands of the SeNB. This enables large volumes of communications.

FIGS. 26 and 27 show an example of the operation of DC in acommunication system of a first modification of the fifth embodiment.The operation when DC is started in this modification will be describedwith reference to FIGS. 26 and 27.

A UE 5205 located in a communication area 5202 of a MeNB 5201 performscommunication of a control signal for mobility management and userpacket data via a S-GW 5206 and the MeNB 5201. When the UE 5205 enters acommunication area 5204 of a SeNB 5203 and the UE 5205, the MeNB 5201,and the SeNB 5203 can perform DC, a reconfiguration to DC (SeNBaddition) is performed, so that two bearers are configured as differentpaths.

For example, a bearer 1 is configured as a path for the S-GW (5206), anS1 (5214), the MeNB (5201), a radio propagation path (5207), and the UE(5205). A bearer 2 goes through the S-GW (5206) and the S1 (5214), andis split at the MeNB (5201). One portion of the bearer 2 is configuredas a path for the MeNB (5201), the radio propagation path (5207), andthe UE (5205). The other portion of the bearer 2 is configured as a pathfor the MeNB (5201), an X2 (5215), the SeNB (5203), a radio propagationpath (5210), and the UE 5205.

Herein, if the UE 5205 does not establish synchronization with the SeNBto measure the communication quality, the UE 5205 cannot actuallyperform data communication. Also, the UE 5205 cannot recognize thecommunication quality of the radio propagation path 5210 when the bearer2 is separated.

The eNB#1 is replaced with the MeNB and the eNB#2 is replaced with theSeNB in the same method as the method described in the fifth embodiment,thus enabling not only the MeNB during in communication but also theSeNB that is adjacent to the MeNB to receive an SRS in advance. As aresult, the SeNB 5203 can transmit data immediately without waiting fora confirmation of the quality of a radio propagation path when startingDC.

The MeNB 5201 can start DC without waiting for a confirmation of thequality of the radio propagation path after determining a ratio ofseparation of the bearer 2 in consideration of not only a receptionresult of the SRS 5208 that the MeNB 5201 receives but also a receptionresult 5213 such as the reception quality of an SRS 5212 at the SeNB5203, which the MeNB 5201 receives via X2 (5215).

The SeNB 5203 can also receive the SRS 5212 to accurately detect atiming difference between the MeNB 5201 and the SeNB 5203. Throughnotification of the SRS reception timing information of the SeNB 5203, avalue of an arrival packet ordering (reordering) standby timer in anuplink PDCP in the MeNB 5201 can be set in consideration of a backhauldelay when DC is started. The SRS reception timing information may benotified together with the SRS reception result 5213.

Although it has been described that a DC start is triggered when the UE5205, the MeNB 5201, and the SeNB 5203 are capable of DC, specifically,at least one of four conditions (1) to (4) below is required.

(1) A time when the capability of the UE 5205 corresponds to DC.

(2) A time when both the MeNB 5201 and the SeNB 5203 can each configureDC.

(3) A time when a transmission delay of an available backhaul such as X25215 is within a DC permissible range.

(4) A time of the detection that the UE 5205 is located within or nearthe coverage areas of both the MeNB 5201 and the SeNB 5203.

Although description has been given of the example of architecture 3C,also in architecture 1A, the SeNB can be notified of SRS config 5216 viathe X2, S1 (MEE), or central entity to transmit data immediately withoutwaiting for a confirmation of the quality of the radio propagation pathwhen starting DC.

Although the addition of a SeNB has been described above, the sameapplies to a change of a SeNB. The MeNB notifies a target SeNB (T-SeNB)of SRS config for configuring an SRS that can be received simultaneouslyin advance, so that the SeNB can transmit data immediately withoutwaiting for a confirmation of the quality of a radio propagation pathwhen changing a SeNB.

Although the MeNB notifies the T-SeNB of SRS config in the descriptionabove, the S-SeNB that is a source may notify the T-SeNB of SRS config.

Sixth Embodiment

A problem to be solved in a sixth embodiment will be described withreference to FIG. 28. FIG. 28 shows the concept of the problem to besolved in the sixth embodiment.

FIG. 28 shows a state in which a UE indicated by reference “5305” amonguser equipment devices (hereinbelow referred to as “user equipments(UEs)”), which are communication terminal devices, is located within thecoverage of a cell 5302 in which the UE can transmit and receive radiowaves of an e-NB#1 (hereinbelow referred to as “S-eNB”) 5301, which is aradio wave base station device being a handover (HO) source. The UE 5305performs a HO 5307 to be located within the coverage of a cell 5304 of aradio base station device (hereinbelow referred to as “T-eNB”) 5303,which is a HO destination. The UE in this state is a UE 5306 indicatedby reference “5306”.

As described in the fifth embodiment, an SRS is a cell-specific signalin the current 3GPP (see 5.5.1.5 of Non-Patent Document 14). The T-eNB5303 thus cannot receive an SRS of a target UE until the handovercompletes, and starts out late the procedure (scheduling) of allocatingresources such as frequencies or timings to the respective UEs based onthe reception quality.

The S-eNB 5301 measures the reception communication quality in the cell5302, in the coverage of which the UE 5305 that is a HO source islocated, and performs scheduling in the same cell. The T-eNB 5303receives no SRS 5309 from the UE 5305 and does not perform scheduling.

The T-eNB 5303 can only receive an SRS from the UE 5306 after HO, andaccordingly, cannot start accurate scheduling that reflects frequencycharacteristics early for the UE 5306 that has performed HO to the T-eNB5303.

Particularly in the operation of a large number of small cells, whoseradius is small, a small cell is repeatedly changed in a short period oftime when the UE moves. When the T-eNB performs scheduling for the UE5306, the UE 5306 has possibly moved to be served by another cell.

Proposed as the method of solving these problems is a communicationsystem capable of starting scheduling by the T-eNB 5303 early by makingan SRS specific not to a cell but to a UE.

FIG. 29 shows an example of the sequence of an SRS reception process ina communication system of the sixth embodiment.

In steps ST5402 and ST5403, the UE exchanges packet data with the S-GWvia the S-eNB.

In step ST5401, the S-eNB transmits a measurement control (MC) messageto the UE to obtain reception quality. The UE measures the receptionqualities of its own cell and the neighboring cell based on theinformation contained in the MC message, and in step ST5404, transmits ameasurement report (MR) message to the S-eNB.

In the sequences described above, the S-eNB that has received the MRmessage in step ST5404 determines whether to start HO in the procedurefor determining whether to perform HO in step ST5408. In thisembodiment, the S-eNB determines whether to start an SRS in step ST5405before the HO start determination in step ST5408.

If the CRS received quality (RSRP, RSRQ, or both of them) reportedthrough the MR message of step ST5404 or another RS received quality issmaller than a threshold Th1, the S-eNB judges that the S-eNB isunlikely to perform HO to an adjacent cell and waits for an MR messageof step ST5404 again.

In the determination whether to start an SRS in step ST5405, the S-eNBdetermines whether the reception quality of the neighboring cell, whichhas been reported through the MR message in step ST5404, is greater thanthe threshold TH1. If the reception quality is greater than thethreshold TH1 (if Yes), the S-eNB judges that it possibly performs HO tothe neighboring cell, and in step ST5406, transmits an SRS receptionstart instruction message including SRS Config to the T-eNB. Uponreceipt of the SRS reception start instruction message of step ST5406,in step ST5407, the T-eNB starts receiving an SRS.

Although description has been given of the example in which the S-eNBdirectly notifies the T-eNB through X2 signaling, the S-eNB may notifythe T-eNB via the MME through S1 signaling.

After transmitting an SRS reception start instruction in step ST5406,the S-eNB determines whether to perform HO in the HO start determinationof step ST5408.

The subsequent HO sequence is the same as the current sequence.

In this embodiment, the SRS start determination of step ST5405 isprovided separately from the HO start determination of step ST5408, thusenabling the reception of an SRS in step ST5407 before HO.

If the S-eNB determines “Yes” once in the SRS start determination ofstep ST5405 and then determines in the HO start determination of stepST5408 that HO is not to be performed, when receiving an MR message ofstep ST5404 again, the S-eNB may perform the SRS start determination ofstep ST5405 again and may or may not notify the SRS reception startinstruction in step ST5406. Providing no redundant start instructionalleviates the processing load of, for example, a central processingunit (CPU). If the S-eNB determines “No” in the SRS start determinationof step ST5405, the S-eNB enters the MR message standby state of stepST5404.

FIG. 31 is a diagram for describing a difference between an SRSreception start threshold and a HO start threshold with respect to ameasurement report value.

A threshold Th1 for starting an SRS in an embodiment of the presentinvention is provided apart from a threshold Th2 for starting a HO.

The S-eNB may set the threshold Th1 to a value smaller than thethreshold Th2. This setting enables the T-eNB to receive an SRS before aHO, thus enabling the T-eNB to perform frequency scheduling early.

The threshold Th1 is set to a value smaller than the threshold Th2above, the threshold Th1 and the threshold Th2 may be set to the samevalue (Th1 =Th2). In this case, an SRS reception start instruction(including SRS config) is notified in the SRS reception startdetermination, and also, a HO request is notified. The SRS receptionstart instruction and the HO request may be provided in one message.

Although the T-eNB starts receiving an SRS later in the case where thethreshold Th1 and the threshold Th2 are set to the same value (Th1 =Th2)than in the case where the threshold Th1 is set to a value smaller thanthe threshold Th2, the T-eNB can start receiving an SRS before the HOcompletes (RRC Connection Reconfiguration Complete) in step ST5414. Inaddition, the determination procedure by the S-eNB can be alleviatedmore than in the case where the threshold Th1 is set to a value smallerthan the threshold Th2.

When the UE 5305 moves very quickly relative to a cell size, the T-eNBthat is a moving destination may not be able to perform schedulingeffectively even if it can receive an SRS. In such a case, the SRSreception start instruction message, HO request message, or any othermessage, which is transmitted from the S-eNB 5301 to the T-eNB 5303, mayinclude the speed information about the UE 5305, for example, themobility state of the UE (high, medium, normal), the number of handoversor cell changes (the number of handovers or cell changes per specifictime is also effective), a GPS position change (a position movement perspecific time is also effective), and a time of stay in every cell, sothat an SRS reception process is not performed. The UE can be restrictedfrom transmitting an SRS 5309 while moving at high speed also when theUE is being served by the T-eNB 5303.

The trigger for performing the SRS reception start instruction describedabove is determined by the S-eNB 5301 based on the reception qualityreported from the UE. Alternatively, the UE 5305 may determine thetrigger and transmit a determination result to the S-eNB 5301, and theSeNB may then instruct a start of the reception of an SRS.

For example, the UE 5305 may include the information indicating whetherthe reception quality per cell is not smaller than a predeterminedthreshold in the MR and then notify the MR.

If the reception quality of a neighbor cell is not smaller than apredetermined threshold, the UE 5305 may include an SRS receptionrequest indicating that the SRS should be received per cell in the MRand then notify the MR.

When the reception quality exceeds a predetermined threshold, the UE5305 may notify that the reception quality has exceeded thepredetermined threshold together with an ID for identifying a targetcell, apart from the MR.

As a result, the S-eNB can reduce the load to determine the receptionquality in the MR.

It has been described above that the SRS reception is started foranother cell on the premise that the UE has transmitted an SRS based ona UE-dedicated parameter. The procedure in which the start of the SRStransmission by the UE is determined will now be described.

The UE consumes transmission power to transmit an SRS, and therefore, itis effective for the UE to transmit an SRS only, for example, before andafter performing HO or to make the SRS transmission interval longeronly, for example, before and after performing HO.

In the SRS start determination of step ST5405, the S-eNB determineswhether the CRS received quality (RSRP, RSRQ, or both of them) of itsown cell, which has been reported in the MR message of step ST5404, oranother RS received quality is smaller than a predetermined threshold(for example, smaller than the threshold Th2), or whether the receptionquality of any other cell is greater than the threshold Th1, in additionto the procedures described above. If the determination result satisfiesany one or both of the above, the S-eNB judges that the UE is highlylikely to perform HO to a neighboring cell and notifies the UE of atransmission instruction including SRS config.

The S-eNB may include SRS config in an RRC connection reconfigurationmessage of step ST5417 and then transmit the message. As a result, theUE starts transmitting an SRS or transmits an SRS more frequently.

As an example timing at which the reception of an SRS is started, theT-eNB 5303 receives the SRS 5309 immediately after receiving the SRSconfig 5311 of the UE 5305 and performs scheduling. Alternatively, theT-eNB 5303 may receive the SRS 5309 from the UE 5305 at least oncebefore scheduling.

Alternatively, the T-eNB 5303 may receive an SRS from the UE 5305 atleast once before transmitting HO ack.

Although described herein is the example in which the S-eNB instructsthe UE to transmit an SRS through RRC, the S-eNB may instruct thetransmission through MAC signaling or L1/L2 control signal (for example,PDCCH/EPDCCH).

The instruction to transmit an SRS, which is provided to the UE by theS-eNB, may be effective until an instruction to stop the transmission ofan SRS is transmitted. This instruction may be an instruction totransmit an SRS periodically during a predetermined period.

If being synchronized with the T-eNB after receiving mobility controlinformation (MCI), the UE may stop transmitting the SRS.

The sequence of HO from the S-eNB to the T-eNB shown in FIG. 29 is asfollows.

In step ST5409, the S-eNB transmits a HO request to the T-eNB. In stepST5410, the T-eNB performs admission control. In step ST5411, then, theT-eNB transmits “HO Request Ack” to the S-eNB.

In step ST5412, the S-eNB that has received the Ack transmits an RRCconnection reconfiguration to the UE, and in step ST5413, transmits “SNStatus Transfer” to the T-eNB. In step ST5412, the UE receives an RRCconnection reconfiguration to reconfigure an RRC connection, and in stepST5414, transmits RRC connection reconfiguration complete to the T-eNBas a result of the reconfiguration. This enables the UE to exchangepacket data with the S-GW via the T-eNB in steps ST5415 and ST5416.

The T-eNB may stop receiving an SRS, for example, after receiving RRCconnection reconfiguration complete in step ST5414. The T-eNB stops thereception similarly if HO fails.

Alternatively, the T-eNB may stop the reception at a timing at which theT-eNB receives “SN Status Transfer” from the S-eNB in step ST5413. Stillalternatively, the T-eNB may stop the reception at a timing at which theT-eNB transmits “HO Request Ack” to the S-eNB in step ST5411.

Although the sequence described above is premised on that the receptionof an SRS is stopped after HO completes, in consideration of a failback,the SRS may be continuously received even after HO has failed.

As the method of stopping the reception of an SRS in that case, apredetermined time is reserved with a timer provided, and then, thereception of an SRS is stopped. Whether the reception of an SRS isstopped may be determined by confirming a threshold again after theexpiration of the timer. Alternatively, the reception of an SRS may beperformed until the UE transmits an SRS reception stop instructionthrough RRC or until the serving cell instructs a stop of the receptionof an SRS via X2 based on the neighbor cell search information from theUE.

One additional threshold for determining a measurement result may beadded for use in the determination of whether to instruct a stop of thereception of an SRS. A value that exceeds a threshold earlier than thestart of HO to another cell may be set. The sequence in this case isshown in FIG. 30. FIG. 30 shows another example of the sequence of theSRS reception process in the communication system of the sixthembodiment.

In step ST5501, the T-eNB transmits a MC message to the UE. In stepST5502, the UE transmits a MR message. In step ST5503, the T-eNB judgeswhether an SRS is required, that is, whether to stop an SRS in responseto the MR message of step ST5502. Specifically, the T-eNB judges whetherthe value of the reception quality of its own cell (T-eNB), which hasbeen reported in the MR message of step ST5502, is smaller than athreshold Th3 or whether the value of the reception quality of the S-eNBis smaller than a predetermined threshold. The predetermined thresholdis, for example, the threshold Th1. The predetermined threshold may be athreshold Th4 smaller than the threshold Th1.

If the value of the reception quality of its own cell (T-eNB), which hasbeen reported in the MR message of step ST5502, is smaller than thethreshold Th3 or if the value of the reception quality of the S-eNBfalls below the predetermined threshold, the T-eNB judges tocontinuously receive an SRS and returns to step ST5502 to wait for theMR message of step ST5502. If the value of the reception quality of itsown cell (T-eNB), which has been reported in the MR message of stepST5502, is not smaller than the threshold Th3 or if the value of thereception quality of the S-eNB is not smaller than the predeterminedthreshold, the T-eNB stops receiving an SRS in step ST5504.

The T-eNB may judge whether to accept HO (Handover Request Ack) based onthe SRS reception result of the target UE. In that case, the T-eNB maynotify that “the SRS reception result is not good” as a cause ofdeclining the acceptance of HO.

The T-eNB performs scheduling based on the SRS reception result of thetarget UE.

An uplink transmission power value is adjusted by the SRS receptionvalue (where an initial MCS is included). This is effective in the casewhere eNBs having different cell sizes overlap each other.

The sixth embodiment can achieve the following effects. The channels canbe evaluated early for a target UE, thus enabling early scheduling toimprove frequency efficiency.

Seventh Embodiment

FIG. 32 shows an example of antenna control in a communication system ofa seventh embodiment. This embodiment will describe an example where, ifan eNB#2 5704 that is a handover destination is capable of transmissionand reception (MIMO) through a plurality of antennas as shown in FIG.32, the eNB#2 5704 is configured to receive an SRS before a handover isestablished and can accordingly perform antenna control such as beamformation immediately at the handover, thus leading to reductions in thetransmission powers of the eNB and the UE.

A UE 5705, 5706 in communication in a communication area 5701 of aneNB#1 5703 is located at the area boundary of an eNB#1 5703 and ismoving toward a communication area 5702 of an eNB#2 5704.

The eNB#2 5704 has a plurality of antennas and can control the phase andamplitude of an input signal of each antenna to form a beam 5711 whosedirectivity is narrowed. In 3GPP, however, an SRS is a cell-specificsignal (see 5.5.1.5 of Non-Patent Document 14), and an SRS of a targetUE cannot be received before a handover completes, so that a beam whosedirectivity is narrowed cannot be formed, as described in the fifthembodiment.

As in the fifth embodiment, thus, when detecting that the UE 5705 islocated at the area boundary of the eNB#1 5703, the eNB#1 5703 instructsthe UE 5705 to transmit SRSs 5709 and 5710 that can be received by aplurality of eNBs through RRC and transmits SRS config 5708 to the eNB#25704 via X2 5707, thus enabling the eNB#2 5704 to receive an SRS signalof the UE 5705, 5706.

The fifth embodiment or the sixth embodiment may be applied in aspecific method of the above.

The eNB#2 5704 has a plurality of antennas and can control the phase andamplitude of an input signal of each antenna to form the beam 5711 whosedirectivity is narrowed.

Furthermore, for example, the directivity of a beam is narrowed byadjusting the phase and an amplitude value (=weighting coefficient) ofan input signal of each antenna in uplink or downlink in which thetraining sequence SRS received power is maximized. The antenna after theweighting is used to receive a data portion other than the trainingsequence or perform downlink transmission, thus enabling communicationusing a beam whose directivity is narrowed. The eNB#2 5704 and the UE5706 can thus reduce transmission power because they are capable of goodreception due to the reduced interference powers of another eNB andanother UE.

In the transmission of an SRS by the UE 5705 before HO, when the UE 5705performs transmission using directional antennas whose directions aresequentially changed, for example, when the direction of transmission atθ (t) is changed in time, the UE 5705 before HO may include differentsequence patterns in different directional antennas such that the T-eNB5704 that is a HO destination can specify a directional antenna.

In the transmission of an SRS by the UE 5705 before HO, when the UE 5705transmits an SRS through a plurality of directional antennas such assector antennas, the UE 5705 before HO may include different sequencepatterns in different directional antennas such that a directionalantenna can be specified.

In an example of the method of determining the weighting coefficientdescribed above, the communication area 5702 of the eNB#2 5704 isdivided, and a divided portion with a maximum SRS received power valueis specified per division. The divided portion with a maximum SRSreceived power is divided further, and a divided portion with a maximumSRS received power value is specified. In one method, the procedureabove may be repeated to determine a weighting coefficient.

In TDD, where uplink and downlink share the same frequency band, thisembodiment is effective for downlink transmission. In frequency divisionmultiplex (FDD), where uplink and downlink use different frequencies,this embodiment is effective when a difference in frequency-dependentpropagation characteristics is small between uplink and downlink.

Although the embodiment above has described the control of narrowing thedirectivity of a beam, the procedure for collectively demodulating allusers through multi-user MIMO can be performed immediately afterhandover. The relationship among the SRS (S_(SRS)) that is the trainingsequence for all UEs, an impulse response (H) of a channel, noise (N),and a reception signal Y is represented by the expression below:Y=H×S _(SRS) +N

For example, if noise (N) is ignored as in the zero forcing (ZF)algorithm, the UE transmission data can be restored by determining aninverse matrix of H. In TDD, the uplink propagation characteristics areidentical to downlink propagation characteristics. Thus, multiplexing(precoding) the transmission data by the inverse matrix of H enables theUE to receive a signal that is less affected by interference.

The eNB may have directional antennas or a group of directional antennasthat cover the entire communication area (corresponding to thecommunication area 5702 of the eNB#2 5704), for example, isotropicreceiving antennas that have no directivity in uplink reception, and mayhave directional beam forming in downlink transmission.

The reception antenna of the eNB may have isotropic directivity.

A neighboring eNB that is not a serving cell can receive an SRS toderive an angle of arrival (AoA). A plurality of eNBs whose locationsare determined can measure the AoA to perform trilateration, thusdetermining the location of the UE without using a global positioningsystem (GPS).

Although the example using the X2 interface 5707 has been describedabove, the transmission may be performed by an S1 interface (via theMME) or performed via the central entity as in the fifth embodiment.

Although the description has been made in which a handover destinationis an eNB, the same applies to the case where a relay node (RN) or aremote radio head (RRH) has a plurality of antennas.

In the case where the UE 5705, 5706 is mounted in, for example, a trainand moves while collectively managing a plurality of users (moving relaynode), the UE effectively includes a large number of antennas for beamformation.

The SRS transmission method, which will be described below, is effectivefor a UE including a plurality of antennas. The SRS is not subjected tobeam formation and is transmitted isotropically. As a result, the eNB#1and the eNB#2 can perform a procedure similar to that of the UEincluding an omni antenna alone to receive an SRS before handover andform uplink and downlink beams promptly.

It is also effective to perform beam formation in which directivity ofthe UE 5705 is narrowed, using a synchronization signal of an eNB thatcan be received by the UE 5705. An SRS is transmitted also using thebeam. As a result, the transmission power of the SRS transmitted by theUE 5705 can be reduced.

The UE 5705 may fail to receive a synchronization signal, and thus, inone method, the location information about the presence of the eNB maybe used to transmit a synchronization signal in the direction in whichthe eNB is located even when the UE 5705 cannot see the synchronizationsignal of the eNB.

During the transmission and reception of a plurality of frequencies bythe UE 5705, the UE may transmit an SRS per frequency by both theisotropic beam and the beam whose directivity is narrowed. This enablesthe eNB to form uplink and downlink beams immediately.

In the case of TDD even with only one frequency available, both theisotropic beam and the directional beam can be transmitted per subframe.

In the case of FDD even with only one frequency available, both theisotropic beam and the directional beam can be transmitted per subframeas in TDD.

The use of the isotropic beam is effective in the case where the eNB isa small cell. The cell has a small radius, and thus, can stably receivean SRS even for a change of the angle of arrival.

The isotropic beam may be used in the case where the UE 5705 moves athigh speed, for example, in the case of a bus traveling around the city.

In the case where a large number of UEs 5705 perform communications athigh capacities, for example, in a case of a bullet train, a beam whosedirectivity is narrowed may be used even if the UEs 5705 move at highspeed.

In FDD of the T-eNB 5704 that is a HO destination, the T-eNB 5704receives an SRS 5710 transmitted from the UE 5705 before HO and thenfeedbacks the obtained terminal information to the UE 5705 through adownlink channel, so that the UE 5705 can transmit the uplink dedicatedchannel information to the T-eNB 5704 that is a HO destination throughbeam forming.

The T-eNB 5704 that is a HO destination needs to judge whether tocorrect a frequency after receiving the SRS 5710 transmitted from the UE5705 before HO. If judging that it does not need to correct a frequency,the T-eNB 5704 can use the SRS Config information received via the X2interface 5707 in the beam forming of a downlink channel.

In the case where the T-eNB 5704 that is a HO destination has aplurality of isotropic antennas such as array antennas, the T-eNB 5704can use the SRS Config 5708 received from the S-eNB 5703 before HO viathe channel 5707 to receive the SRS 5710 of the UE 5705 that is toperform HO, thus calculating propagation characteristics H.

The T-eNB 5704 that is a HO destination can use directional antennassuch as a plurality of sector antennas (including the case where theequivalent directivity is formed by an array antenna) to performprecoding in which directivity is pointed to a place at which the SRS5710 is received at high power, thus performing transmission through thebeam forming 5711.

In the transmission in which the directional antennas of the T-eNB 5704being a HO destination sequentially change their directions at thetimings at which the UE 5705, 5706 transmits an SRS, the direction inwhich the T-eNB 5704 being a HO destination performs transmission iscalculated at a time when the reception power of the SRS 5710transmitted from the UE 5705 is maximized, thus enabling a transmissionthrough the beam forming 5711 in which directivity is directed to thecalculated direction.

Alternatively, in the transmission, the directional antennas of theT-eNB 5704 that is a HO destination may successively change theirdirections at multiple timings of the timing at which the UE 5705, 5706transmits an SRS.

Alternatively, when the SRS 5710 transmitted from the UE 5705 isreceived at least once during a reception period in the direction inwhich the direction antenna of the T-eNB 5704 being a HO destination hasperformed transmission, the transmission through the beam forming 5711is enabled, whose directivity is directed to the direction in which theT-eNB 5704 being a HO destination has performed transmission.

The T-eNB 5704 that is a HO destination may obtain the terminalinformation through a random access procedure for transmission throughthe beam forming 5711. The UE 5705 that is to perform HO transmits aPRACH to the T-eNB 5704 that is a HO destination. The T-eNB 5705 that isa HO destination transmits a random access response to the UE 5705.

The UE 5705 that is to perform HO notifies the T-eNB 5704 of thelocation information on the UE 5705 in the random access procedure. TheT-eNB 5704 that is a HO destination can thus specify the locationinformation on the UE 5705 that is to perform HO in the random accessprocedure to perform transmission through the beam forming 5711 whosedirectivity is pointed to the UE 5705.

The T-eNB 5704 that is a HO destination can receive the PRACH during ahandover to calculate an angle of arrival (AoA), thus enabling thetransmission through the beam forming 5711 whose directivity is pointedto the calculated angle of arrival.

Synchronization can be established by the reception of an SRS duringhandover, and thus, no RACH sequence may be used.

When the UE 5705 before HO moves together with another UE, when the UE5705 is a terminal including a plurality of antennas, or when the UE5705 functions as a repeater, the UE 5705 notifies the T-eNB 5704 beinga HO destination of the location information on the UE 5705 before HO,which has been detected by the S-eNB 5703 being a HO source from the UE5705 before HO, together with the SRS Config (configuration parametervalue) 5708 via the channel 5707.

Thus, the T-eNB 5704 that is a HO destination can receive the SRS 5710transmitted from the UE 5705 before HO to use the SRS 5710 to derive aprecoding matrix, that is, derive a weighting coefficient of an antennafor beam forming. This enables the T-eNB 5704 that is a HO destinationto perform a transmission through the beam forming 5711.

In this embodiment, an SRS from a terminal that is a HO source can bereceived also during MIMO to determine the beam directivity and theinitial transmission power of the terminal, thus enabling appropriatecommunication from the start of HO.

The reception quality in the UE during HO can be improved, thus reducinghandover failures (HOFs) and radio link failures (RLFs).

The method disclosed in this embodiment is applicable to themulti-stream beam formation.

The embodiments and modifications thereof are merely examples of thepresent invention and can be combined freely within the scope of thepresent invention. Any constitutional elements of the embodiments andthe modifications thereof can be changed or omitted appropriately. Thecommunication capability of the UE can therefore be improved also in thecase where a large number of small cells in addition to a macro cell areinstalled and operated.

While the invention has been shown and described in detail, theforegoing description is in all aspects illustrative and notrestrictive. It is therefore understood that numerous modifications andvariations can be devised without departing from the scope of theinvention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   101 CBC, 102 MME, 103 MeNB, 104 SeNB, 105 UE, 1301 coverage of        macro eNB (macro cell), 1302 coverage of small eNB (small cell).

The invention claimed is:
 1. A communication system comprising: acommunication terminal device; and a plurality of base stationsconfigured to perform radio communication with the communicationterminal device, wherein the plurality of base stations include a firstbase station configured to provide an emergency bearer for emergencyservice for the communication terminal device, and when the first basestation in a state of providing the emergency bearer transmits, to asecond base station among the plurality of base stations, a request forexecuting a dual connectivity (DC) for the communication terminal devicetogether with the first base station, the first base station isconfigured to transmit, to the second base station, informationindicating that the DC is made to the emergency bearer.
 2. Thecommunication system according to claim 1, wherein when the second basestation receives the information indicating that the DC is made to theemergency bearer, the second base station is configured not to executethe DC for the emergency bearer in a predetermined case, and thepredetermined case includes a case where the second base station doesnot allow establishment of the emergency bearer.
 3. The communicationsystem according to claim 2, wherein the predetermined case furtherincludes a case where at least one of a status of the communicationsystem and a power consumption of the communication terminal device doesnot satisfy a condition for executing the DC for the emergency bearer.4. A base station configured to perform radio communication with acommunication terminal device, wherein the base station is configured toprovide an emergency bearer for emergency service for the communicationterminal device, and when the base station in a state of providing theemergency bearer transmits, to another base station, a request forexecuting a dual connectivity (DC) for the communication terminal devicetogether with the base station, the base station is configured totransmit, to the other base station, information indicating that the DCis made to the emergency bearer.
 5. A base station configured to performradio communication with a communication terminal device, wherein thebase station is configured to provide a dual connectivity (DC) for thecommunication terminal device, when the base station receives, fromanother base station in a state of providing an emergency bearer foremergency service for the communication terminal device, a request forexecuting the DC together with the other base station and informationindicating that the DC is made to the emergency bearer, the base stationis configured not to execute the DC for the emergency bearer in apredetermined case, and the predetermined case includes a case where thebase station does not allow establishment of the emergency bearer.